And, in fact, it may be a bonus. Less seminal fluid usually means that men can delay ejaculation for a longer period of time. Again, this benefits both partners. It's common for the length of love making to increase as men age. There's absolutely nothing wrong with that.
Some men worry that their orgasms become less powerful with age.
In some cases this may be true, but less powerful does not mean less enjoyable. And men will notice that it takes longer to have another erection after orgasm. In your seventies it may take a few days. But this increase in time in no way reflects a loss of potency, a decline in sexuality, or a loss of sexual drive. As we age both men and women realize that there are other parts to making love other than orgasm.