knee pads are an absolute must scott ...i've started usind a kneel board which is about 2ft square and triple layered with foam ,(similar to a fitness mat.)
it's my knees that are the worst as i didn't use anyprotection early on ..i've had two cartlidge trims and have a split and frayed cruiate(spelling? ) ligament in my right knee (surgeon took photo's of it during the last op)...i can't sit in any sort of position for more than a couple of minutes without having to adjust my legs
hands and back are just generally worn ,i might have got dodgy hands of my dad cos he's had a few op's to release tendons in both hands ....i always say that i'm gonna end up with hands like budgies feet

you need to generally look after yourself ,not just in plumbing but in any construction trade as they are all physically demanding...

clayton's got it spot on imo about the majority of younger people (not all ,but most) wanting easy money for little amount of graft ...i call them blairs children,and that's probably one of the reasons for there being a shortage of most construction trades.....