Since I was a small kid, Jake was my best friend. We were the same age and spent a lot of time together. Every summer we spent a week in my parents summer place and went swimming, playing, and biking around the countryside. One summer we discovered 'playing doctor' with Jake. I had already been wanking for some time, and was always curious if Jake did the same, but never dared to ask before that summer. We had been swimming naked and I was so thrilled about seeing him nude that I proposed we could get naked again and compare our dicks. So we did, which became to be a beginning for lots of sexual play over the next few years. I was always the more active one proposing things to do, but Jake was always happily playing along. 'Playing doctor' was always the most popular one, and over time we made it quite professional and even gathered some real materials to complement my toy doctor kit.
Jake also had a sister Emily who often wanted to spend time with us, but Jake wanted to spend time 'between us boys' only, so we rarely did anything with Emily. Sometimes I was wondering how would it be to play doctor with a girl, but for some reason we never even discussed it with Jake. But when I turned 13 I started to become more interested in girls. Many of the girls in my class started to develop that year, at least many started to have small puffy breasts that were clearly visible when they wore tight t-shirts, which made me curious about their development and bodies. I was trying to imagine how did the girls of my age look 'down there' and how many also had some pubic hair already. Apparently I was starting to devleop as well. I started wanking almost daily and started to develop all kinds of crazy fantasies in my head. After the school doctor physicals that year I started fantasizing about playing doctor with girls. But of course I had no chance, so the best I got was an occasional doctor play with Jake.
Then all by sudden it all changed that summer. Emily had sometimes spent a few days in our summer place as well. Always at a different time than Jake was there, though, to make sure there was no fighting between them two. For the last few years she had not come at all, but this summer she told she would like to come again. First I did not think much of it, but then I realized this might be my chance! I had really become girl-crazy by then, so if I could at least sneak a peek of her when we were changing clothes for swimming or something that would be nice! I had no idea what would happen, but I was really excited!
Then when she came to our place I was like OMG! She wasn't very tall or anything, but she was really slender and had really nice puffy ass. She had long brown hair tied up into a ponytail and nicely tanned skin. Boy I had a hard time behaving normally, as I immediately started imagining her naked and of course got a boner. Later when we went swimming I tried to see her changing into swimwear but didn't succeed, but I got to see her in wet swimsuit and realized that she actually didn't seem to have much breasts yet. Nevertheless I had hard time controlling my weenie, and spent most of the time deep in the water to make sure nobody would see my 'tent'.
The next day was quite similar, real fun time together but no naked bobies unfortunately. I was really getting crazy about seeing Emily naked, so once we were bored and thinking what to do next I just bluntly proposed that we could play doctor. To my surprise she didn't reject the idea. I have no clue if she also thought that the doctor game would mean also getting naked in front of each other, but at least she tried to ask how do you play doctor, but I refused to give any details. I just told her that I had an old doctor kit we can use and that she will be the patient first so she will get the idea. She was happy with the proposal, so we went to our cabin and I pulled my doctor kit out. I told her to go out while I get ready.
While she was out I put on my white jacket (which was quite tight for a 13 year old given it was kids' toy kit) and a stethoscope around my neck. Then I called her in. I asked all kinds of questions first and then explained to her that I would do a complete head-to-toe check-up. Then I told her to strip down to underwear. She didn't resist at all, and pulled down her shorts and took off her t-shirt.
My weenie was hard as rock and I had hard time keeping it still in my pants. She had almost no breasts at all, but her nipples were really large and a bit brownish. First I checked her ears and mouth pretending to be a real doctor, and then I put stethoscope on her chest to listen to her heart and lungs. I accidentally touched her nipple a couple of times, but she just giggled and didn't resist. So I decided to move on and told her that for the rest of the exam she would need to remove her panties as well. She looked at me and told me she knew the whole doctor thing was because I just wanted to see her naked, but then she pulled her panties down anyway. She didn't have any pubic hair yet and her pussy was just a simple slit, but it was already more than I had dreamed for.
I told her to hop on the bed which was my 'exam table' and lie on her back and pull her knees to her chest so that I could have a look between her legs. She giggled and told me that was gross, but then finally she pulled her legs up anyway. I was like OMG! She was still pink all over and I couldn't have believed that girls had all that hidden between their legs! Her vagina hole was also all open and visible. I had always been fascinated by the thought of girls having a hole in them and wondering if it really looked like a hole you can look into and now there it was right in front of my eyes. It was quite small but clearly open in the middle and I was like wow that's where the penis is supposed to go in. I touched her here and there and she told me it tickled. Eventually I even put my finger maybe an inch into her and it felt warm and slimy inside her. I 'examined' her for really long time and she did not resist at all and I just could not get enough of what I saw between her legs. I was so excited and I had a boner like never before. Eventually I told her that everything seemed to be ok and that she could get dressed. My heart was still pounding when she started to dress up and I was like that was the best experience of my whole life!
Once she got dressed I went out and she called me in for a check-up. She told me to undress to my underpants and then did the same procedure. My penis was fully erect right from beginning and I realized she kept on looking at the hump in my underpants seemingly very curiously. I don't know if she had ever seen a boy naked, but she was definitely keen on seeing me! So soon she told me she needed to check my privates and that I would need to get fully naked. So I dropped my pants and my weenie jumped up like a spring. Even though I was already 13 my penis was only maybe two inches long when soft, but in full erection it was at least four inches long. I also had some light hair down there already, so it probably looked bigger that she had expected or seen before. She was just staring at it in complete awe, so I jumped on the bed and told her that now she could 'examine' me. I showed her how to push and pull the foreskin back and forth so she could 'check me there as well'. Apparently she had never seen that being done so she seemed truly amazed. She stroked me only a few times before I orgasmed, but only a few drops came out still at that age. She was like wow but seemed to know what just happened! After that she told me I could get dressed. So I wiped my belly with a napkin and jumped up. I was still burning for more, but did not dare to propose anything, so we closed the game.
Later the same evening when we were going to bed she started asking me about all kinds of boy stuff. We also discussed how boys and girls do 'it' and it felt so exciting to even talk about the subject and eventually we ended up showing each other. We talked late into the night and had such a great time. Later that year we started emailing each other and she told me (and then later on showed me) when she started to grow hair between her legs and when she started her period. But a bit before she turned 14 it just somehow stopped. We were still friends but did not discuss boy-girl stuff anymore. But in many ways she was my first girl and I still often think back to those times.