weights to use , well their is no real set limit , whatever you can manage to lift , start off at a limit that you think that you can handle , not too heavy and not light , as long as you still manage to do the correct form , from their when you think your right up the weight to a bit higher again as long as you can still manage the correct form
how often you should work out , about every 2days should be fine , give your body a day to recover
forget about the supplements just yet , concentrate on getting your diet right
what's your diet like at the moment , what do your meals consist of
in the grand scheme of things , your age group means nothing , depends on your fitness level , their is so set formula saying at this age group you need to be lifting this weightage , everybody is different , start off with the babysteps and make your way up , it all takes time