Good advice AA62. I wish I had applied and joined earlier at 18 rather than 22.
For tl202 - I would advise going for it as early as possible. You can always dig when you leave and I know some guys have done a bit of digging at old aircraft crash sites and also when stationed at Akrotiri - so you could carry on as an amateur digger after you join. If you fail your selection then you have a further chance to go away and come back - leave it too long and you'll only get one shot.
Good luck
LJ