I have a serious intolerance for zinc and magnesium.
In my teens, I could cum as much as 1/3 cup and squirt up to 3 meters(6.5ft). I had a girl that like to measure my loads and my dick size before, during, and after fucking.
After getting older, and having health problems, I can barely work out two table spoons full after holding back a week and edging for up to two hours. My orgasms have went from nearly 30-45 seconds to 5 to 10 seconds. Once that first shot is out, usually a few inches, it's over. The orgasm dies quick and then I just dribble out the rest of my cum.
My orgasms seem to feel better when I'm with someone and they are longer. Bating is just pointless, unless I'm hurting for a good suck n fuck. It can be as little as a few drops from beating off.