just had a thought. i could get it up loads until like 2 months ago (when i passed my driving test/ school ended) and i was wondering could a lack of exercise be related? and can that like strongly influence it? i drive everywhere atm. i walk about 1/10 as much and hardly cycle. could that seriously be related? a no bs assesment would be nice!
Back to before..
Certainly exercise is good for you generally. It will make you more fit and healthier, and it also helps with depression. Even apart from the erectile dysfunction, you should try to exercise more.
Assuming you're reasonably healthy otherwise, it shouldn't effect your erections that much. It's probably more of a function of you just maturing more, and spontaneous erections tend to happen less and less as we get into our late teens, as our brains get used to all the testosterone flowing in our veins.