At age 33 now I have to admit something. My sex drive is noticeably declining. When we were teens, just thinking about sex or seeing a girl's nipple poking through a shirt would give you a boner that was hard to get rid of. And of course that was the time the teacher would call you to the front of the room. ;-) Now even porn doesn't arouse me much anymore. I don't know if this is a bad thing necessarily. Maybe it's good, and it just frees up part of my brain to think about more productive things. I hope this is just a leveling-off and not a steep decline. Otherwise by 45 I'm going to be impotent. I still get very aroused when I'm physical with a girl, but merely thinking about it or seeing a nude female body doesn't get me there anymore. Which is a huge difference from my younger days.
