I am also 71. Yes, my volume of semen has decreased, but still a decent amount I think. Sometimes it seems more clear than white, but doesn't concern me. Things change with age, diet, meds, etc. Be sure to stay hydrated. How often do you orgasm and ejaculate? I average 3 or 4 times a week, usually by masturbation. Orgasms are still very pleasurable. If it really concerns you, ask your doctor, but I would think it is a normal change.