At 77, I must be the oldest poster to this thread. I agree with many of the thoughts regarding masturbation, as well as jelquing, being healthy 'activities' for the penis. I was married 29 years to a female and continued jackingoff during these years, although not as often as during single life. I've never noticed any decrease in sexual drive and accompanying cock manipulation as I grew older, except during my early 70s when I actually stopped having nocturnal hardons and waking up with it erected. I began stretching and jelquing exercises three years ago and my nocturnal hardons have returned, as well as making my dick thicker (really heavier) than before, keeping me more 'aware' of it throughout the day. Although I had stroked to climax daily before PE, since I became regular with it, my stroking to climax has decreased to 2 or 3 times a week. It's as though jelquing fulfills my desire to 'play' with it and it's not as important to shoot off as before.
My prostate examinations have reported my PSA at a high of 3.17, and generally even below that figure. I attribute my healthy prostate to keeping the ejaculate flushed out of it, thus keeping it firm.
I began lifting in my early 30s and running in 1967 and was regular with both forms of exercise until Dec. of 2002, when I had to quit both because of Myasthenia Gravis, which is now under control. I, like donkeyboy9, have always watched my diet and kept my weight to 150-55, at a height of 5'6". My erected cock has increased from 5.75 girth to a full 6 inches, thanks to jelquing, but I've been disappointed in length increase. I pass the 7 inch mark by just a fraction, nothing like that of donkeyboy with his 9! Awesome!