What someone can lift is in direct proportion to how much they work out, there is no set limit.
The best way to find out what your limitations are is to start very light and increasingly put more weights on until you are just about able to lift it properly without major strain on your back.
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This really goes for all ages, but since you're asking, I think you should be lifting enough so you can do 3 sets of eight reps with good form (very important). And also, make sure you are doing exercises that are effective ( that work the most amount of muscle groups, in other words). Exercises like that would be dead lifts, bench press, military press etc. And by doing that, you should be seeing results in about 12-15 weeks (depends on how fit you are). Hope that helped!
16 years old girl should lift between 25-40lbs for dumbbells. She should bench at about 135lbs.