If your character's starting off at level one, they're really only getting started with adventuring. You can let that be reflected in their backstory.
If you want to play a badass, starting above level 1 is allowed, though probably not recommended for new players still learning the rules of whatever system you're playing.
I still maintain DND is kind of a bad first rpg. It's extremely idiosyncratic in its rules, and it's also a dream crusher that squeezes the creativity out of new players.
More people would be happy with Fate.