I'd suggest that it's an illusion, Big Drum Stick. In your youth you were probably not only in better physical shape but your body had not yet 'filled out' with your true adult proportions.

As you age, gravity and lifestyle take over to loosen things up a bit and fat gathers in odd places (such as in the lower abdomen at the base of your penis) making your penis look shorter.

Don't worry. It's still there, in all it's former glory.

If anything, your junk will actually hang more in its relaxed state as you age.