I'm quickly coming up on 50....and so far, I've been blessed.
My aches & pains tend to be of the dull, annoying sort you usually get from doing more of something in one day than you've done in the past six months. Stay off the lader for a bit- then spen a day changing lights...I'll feel it at the end of the day!
More annoying has been a lesser amount of flexibility and agility.
Our trade isn't one that requires extreme physical strength or stamina. Unlike some trades, we don't spend all day in one position. And, as we gain experience, we seem to spend less time pulling wire and more time trouble-shooting and hooking up controls.
Doggz, what you describe sounds like a simple case of you're developing some muscles you never knew you had. The same thing happens in boot camp; all sorts of mystery aches show up as you start doing things you've never done before. Something as simple as hanging a radio on your belt will cause some stiffness, until your body adjusts.