It's really your choice and if you feel like you're ready. Also, talk to your Mom. Does she think you're responsible enough? And also maybe ask her how old she was when she babysat. If you both agree that you're responsible enough, then go for it! Ignore what your sister says. It never hurts to try!
My whole goal in life is to get AlphaT to debate Teh_Skittlez as an Atheist and for Teh_Skittlez to debate AlphaT as a Christian.
That awkward moment when you realize that you couldn't see that amazing debate because you're not old enough to see the P&R section... -.-