This happened a couple of years ago when Lucy was younger, staying over for the weekend whilst at college.
Like most older guys, there comes a time during the night, usually about four am. for me anyway, when I wake up and have to take a leak. Well I had just gotten back from the bathroom and because it was a warm night, I just lay on top of the covers in my boxers starting to drift back to sleep. My imagination must have kicked in because old faithful had stayed awake and started hardening. Well you know that when that happens, you just have to stroke it a little, and it gets harder and bigger and pretty soon you have got your hand wrapped round it going for gold.
So I am lying there slowly jacking with my eyes closed immersed in a fantasy, when I hear a gasp from the doorway. It's just light enough to make out my grand-daughter Lucy standing there watching me. The shock of being caught like that made me cum instantly and three big spurts flew up my stomach and chest. Instead of running away, Lucy came up to the bedside and said Wow Grandad, that was so hot!
I thought I was going to have a hard job explaining this, but she sat on the edge of the bed, looking at my still hard cock and the trails of cum on my body. She said 'I've never seen a man cum before, I didn't think it shot out like that.....can you do it again? When I make myself cum, I can do three or four straight off'
I thought, now is my chance and said 'I guess I can come again if you rub it for me'
Lucy gently curled her fingers round my shaft and started to stroke slowly, but I could see her left hand reaching under the tee shirt she was wearing and touching her pussy. My hand joined hers under the tee and found her hard clit, she had a finger deep inside her pumping in and out in time with her hand slipping up and down on my wet cock. It did not last long for either of us, I came again spurting just before she had a shuddering climax.
Well that was two years ago, and I'm glad to say it has been repeated many times whenever Lucy stays over with her loving Grandad.