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'd never recommend playing dnd 5e at level 1, even for beginners. Level 3 is where classes get their basic identity and you don't instantly die to everything
The first few levels should be thought of as a tutorial, where there is no true peril no matter what enemies you face.
It's useful to get a feel for a new character before you start piling on all the details of class skills.
But the peril is highest in those first few levels as a strong breeze will kill a level 1 character. I also think it is hard to get a feel for a character if they lack eveything that defines them class-wise imo
Level 1 might be a good place to start for someone who's never heard what a TTRPG is. Your abilities list is small enough that you don't need to think hard about what you can do for every round of combat, and you probably have very few out of combat abilities so you just roll for it.
That said, it's also really fucking boring. If you want them to have a good time, they better get through the first few levels quickly.