"Someone who is soaked in "zema" (Forbidden sex), old age jumps up on him" (Shabbos 152a). In other words, if you're 50 and you feel like 90--- Oh oh!!!
"Thinking of (Forbidden) sex is more damaging to the body then actually doing it" (Yoma, beginning of 29).
"Sex makes the body weak" (Brachos, 57b).