Totally normal to masturbate. Orgasms feel great and have health benefits. Not sure if you can increase semen production, but you should make sure to stay hydrated. Water intake is important. Also, at 71 myself, I have noticed the volume of my ejaculations is less than when I was 20-50 yrs old. Try "edging" some when you masturbate...stop just before you are about to cum, then repeat 2 or 3 times. When I do this and finally release, my orgasm is more intense and my ejaculation is stronger and the amount of semen increases. Hope this helps.