Time makes all things better. However, you keep playing with that hose and you will wear it out

At eighteen your cock is as big as it's going to get. But don't worry, yours is bigger than most men's. After you pass age forty it will probably start to get slightly smaller, most men's dicks do. But it won't get a lot smaller. At sixty-eight mine is about half an inch shorter than it was when I was eighteen. That doesn't worry me because it still gets hard and it still squirts jizz and that's all that matters.

At 59 my cock doesn't look appreciably different than it did when I was 19. It gets just as hard, is just as sensitive, and gives my partner orgasms just as well as it ever did. Perhaps the only minor change is that I'm not hard 20 hours a day any more but that's actually a good thing and more mental than physical. I don't think you have to worry about your cock fading with age.