if you learn on a heavy bike then you'll will be a better rider in my opinion when you get a lighter one,plus lighter bike usually wont last as long as a hefty steed.
my bikes are setup with strength and longevity in mind,i reckon my simtra must be around 12kg in weight if not more and i'll tell you something ,i havent changed a part in 4months or more because i've broken something from riding hard ,yeah im not a go big or go home type of rider but i am a bit rough on the landings like.
so personally i would say i wouldnt worry about weight too much mate.well thats my little rant over lol,cheers ,steve