I can tell you exactly why your penis seems like it shrunk. When men hit a certain age, depends on the guy, but they begin to fill out, grow muscle, get more mass in places they didn't before, some is noticable, some isn't. Your penis didn't shrink, the surrounding tissue and area increased in bulk, causing it to seem like your penis isn't as big as usual. It's normal and unless u starve yourself, it'll stay that way. My penis used to be a little over 11 inches long and 7 inches around. Thats when I was like 16-18. I'm 22 now and my size is only bout 10.6 inches long, but the girth remains the same. It happens to all guys unless the remain very skinny. How to make it bigger past that, I have no idea. Just don't do anything that could make you lose your penis.