its only wants to be light if you start of at a young age such as 5-6 years old because of strenght and so on too practise the main balancing but as you grow you'd get a bigger bike but if your used to a light bike yeh i think you'd get a lighter bike again when you've grown but like when most people start they usally get a cheap bike thats oki like a monty 219 alp or magura, onza comps, blades or maybe something cheap as like the old onza tv but as you'd learn on something like that you'd want to upgrade it as your skills become better such as when you learn to gap and say you've got standard vee pads or hs33 pads your going ot go looking for advice and thats probs how people end up on here because of tips and wikis to just help you out as you learn.
But starting off on a light bike will give you more abillity to learn things easyier but i'd think it'd be better to learn on something a bit clumbsy/heavy and then upgrading it as parts break or to make the bike feel better after reading about topics on here such as handle bar and stem recomondations and upgrading to a stronger chain then a free wheel with more engagments not like from an acs to an echo sl just something like a tensile 60 click and just basically keep getting better parts once they break or get worse soo you can keep progressing till you end up with a full spec koxx or monty but as i said at the begining if you start off at a young age like adam morewood because his already starting comps and things he will just get a lighter bike again when he needs a bigger frame than his monty because of him always using a light weight bike and also the fact that in comps you dont want a heavy bike to lug around do you.
My mate went straht from a normal monty 219 magura to a whole new gu le with a rear chris king and i said why did you get that back hub cause its got that much more than the standard free wheel he had on his monty like if it was me i would of got a profile and also saved money if anyone gets what imean its not me just being jelous or out its just why have a ck with 72 eps from a free wheel with like 36 eps the only better thing for him now is a 108ep ffw instead of it being a 72ep ck hub from a 48ep profile, not like its really important but it makes your power get to the rear wheel quicker meh you should get the point of what i've said
EDIT: dont know where to put any full stops sorry