Had been to football practice when this happened.
I was around 16 at the time and came home after football practice. It was still summer before school started and my sister and her girlfriend were at the house. Practice had just started days earlier and I was really feeling it. Sore all over. My sister's girlfriend, Missy, had a thing for me at the time. She was around 15 at the time and very pretty. She could see how sore I was and she took advantage of it by asking me 'Like a massage'? I asked back 'You really mean it'? She said 'Sure. I'll be glad to'.
I took her up on it. We went to my room and I headed to the bathroom and changed to a pair of shorts. I laid on my bed face down and Missy came over and started rubbing me down. I remember her hands felt great on my sore body. When her hands got to my upper legs and she was working with a hand between my legs, things began to happen. Remember, I was a young 16 year old boy and having a girl's hand so close to my 'privates' like this caused my cock to start to twitch and tingle and swell. She finished this area and worked on my back and arms.
When it was time to turn over, I was hoping my shorts would hide everything. She started at my feet and worked her way up. Soon, her hands were again on my upper thighs and again, it had the effect on me. It wasn't long and there was no way that my shorts could hide things. I soon had a full erect cock. About that time, she looked at it and then looked up at me with a little smile on her face. I told her 'I can't help it'. She just smiled at this. She went back to looking at my crotch area again. All this did was make me even harder. She looked back at my eyes and ask 'Can I touch it'? I said 'If you want to'. She then put her finger tips on it and as she did, I let out some soft groans from the feelings I was having. She ran her fingers on it awhile and then ask 'Want me to massage it too'? She was old enough to know about boy's jacking off. I said 'Yes, if you want to'.
She then pulled my shorts down. I was so excited. There I was laying there showing my cock to a girl for the first time. She put her hand around it and slowly started stroking it. I laid there looking at her groaning with pleasure. It wasn't long and I gave her one heck of a cum shot. When it happened, she jumped back saying 'Oh my gosh' and just held my cock watching me shoot. Cum ended up all the way up to my neck and then covered my chest and stomach. Missy then went to feeling the cum on her finger tips.
After this, we did become boyfriend/girlfriend and these hand jobs became a regular part of our relationship. Both ways. It was wonderful. And yes; we did end up doing other things also.