Okay, I guess I've been called out on this one, so I'll give my limited knowledge. I haven't exactly been on T a long time... about 16 months, I think, but I don't think there's anyone on here who's really been on it too long with the exception of Dennis or Mister (who seems to be MIA). I've only known one guy who was on T into old age... I think he was about 65 when I knew him, and he just looked like any other little old man, albeit shorter. The balding part doesn't necessarily happen when you get older; I'm losing my hair already. As I've said before, hair loss has to do quite a bit with genetics, so if your brothers or uncles started losing their hair around 25, you're likely to see it around that time (or once you start T, if it's after that). My dad lost all his hair at 17; my oldest brother's hairline was receding around 20. I count myself lucky that I still have a full head of hair at 27, despite the fact it's thinning dramatically.
As for going on and off T, I've done it twice, for 4 months each time, though not by choice. What I experienced was fat redistribution to what it had been before; my facial hair thinned out and became softer, and body hair diminished, though not to what it was before T; periods came back after 2-3 months; voice stabilized, but didn't get any higher; and my moods changed... I had PMDD before T, and of course it came back with my periods, and my bipolar worsened (it gets better, or at least easier to handle, on T). All of this is pretty much concurrent with what I've heard from other guys who've gone off T for one reason or another; there was a TLC documentary on Thomas Beattie in which he talked about losing muscle tone and hair when off T to prepare for his pregnancy, and he'd been on T for about 5 years prior to that.
I imagine that the longer you're on T, the longer it might take for those changes to take place if you have to go off it, but also, I can imagine it would take an even tougher toll on your mental state. For me, being off those 4 months at a time was agonizing, simply because I knew how much better I functioned on T. That said, I should mention that I noticed I had about 1/5 of the energy off T as I had on. It's not a fun thing. Of course, if you've had a hysterectomy, you'd probably have different effects from going off T, due to the lack of massive levels of estrogen.
Hope this helps.
SD