I’m already 27 (in other words, old).
I only did jelq two times for about two months, up to 400 strokes if I remember it right. On the second time I was doing newbie routine and I was on the second last week, when - while stretching - I felt pain on the head and when I pulled foreskin out, there was noticeable red spot. First I just left it like that for a few hours, but then I decided to puncture the spot and it gradually disappeared. But it was scary anyway. After that, I’m not sure I’m going to try any stretching again.
What I meant about possible injury is that “penis pipe warning thing” for newbies. It wasn’t here last time, but now it is and PE exercise isn’t so tempting anymore.
I also have problem with somewhat tight foreskin and I’m treating yeast infection at the moment. I just hope that’s the reason for it (or at least the reason why stretching frenulum didn’t work). It doesn’t stop me using fleshlight, but it seems to weaken my erection a little when foreskin doesn’t move much and stays partly over head.
I gave a little too much with 5.2 girth, 5-5.1 (12,7-13 cm) is more correct. I know that statistics suggest I’m average, but it just seem so small whenever I look at it. If I look at it sideways or just see it from opposite angle head on, it looks bigger than seeing it from above, but not sure if mirror is just making it look bigger. My penis might also have a little weird shape, since width is 4,5 cm measured from above and it does look little flat. It might be because foreskin is tight, so it’s preventing that big vein from expanding near the head.