I agree, the penis itself doesn't really age. Things around it do however... Gray pubes, watch the fat pad, wrinkly skin on legs. That's what you need to watch out for if you're trying to keep things young looking.
I moisturize my hands, tattoos, and cock and balls after I get out of the shower each morning. It helps keep that skin in good condition. I agree that staying in good physical shape and perhaps doing some manscaping will help maintain good appearance for your package.