Yes you are weak. Doing push ups will be the best thing that can happen to you. No point using dumbbells if you can't even handle your own bodyweight.

read this:
http://www.simplefit.org

I don't see a problem with starting weight training young.

The purpose of doing weight training is to stimulate growth.
How is it that weight training can stunt growth when it stimulates more growth hormones to promote growth?
If you're still in puberty, it's highly likely that with weight training, you will grow taller.

This is all true provided that you don't injure yourself, and you increase weight in a well planned manner.

This will stunt your growth:
You weigh 60kg and have never lifted anything besides your school bag. Then the 1st time you go to the gym, you tried deadlifting 120kg.
POP! You heard a pop in your back. Oops, you probably injured your back. And you're in and out of the hospital and in constant pain. <--- So, how to grow taller like this?

LOL! Stunted konon.
Stand next to them, and you'll know there are not short or stunted in anyway. They are just so muscular with a thick torso, it looks stunted on photos only.

It's an optical illusion.