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
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.
Considering that a real world new recruit who's only martial experience is about 8-10 weeks of basic training would probably be a second or maybe even third level fighter, first level characters aren't very impressive. If there's an actual zero next to "Experience" on your character sheet you aren't a grizzled veteran and you haven't seen anything rougher than a barfight. You probably lost that fight, too.
Consider that a level 1 commoner is like... well, let's just say the average American. Not your average gaming enthusiast, of course, but like, one of those folks working down at Wendy's, who probably weighs a little extra and won't take shit from you if you try an' start somethin'. Can probably run a mile in 15 minutes, or 20 minutes if they're in heels, but make that 12 minutes if cops are involved.
Speaking of cops, I feel like they're a pretty fair baseline of what a level 1 fighter would be. You know the type: usually a bit overweight, but they'll still run you down, and you can bet your sweet bippy they know how to use their guns. Some of the sneakier roguish types can evade them, but they do travel in pairs because hell if they're gonna take any chances against the action economy in this world.
Consider then that coming out of basic training, the average male needs to pass a test during which they must be able to perform, in sequence, ~40 pushups in 2 minutes, ~50 sit-ups in 2 minutes, and then run two miles in under 17 minutes, pretty much back to back.
This is in addition to actual skills learned. While most civilians can go to a shooting range and hit a target with a gun pretty well given half an hour of safety training, by comparison, basic training involves multiple hours per day of gun training for 6-8 weeks.
This is for army basic training, your basic-bitch grunt shooty boys, this isn't even the elite marine training or anything which would almost certainly be even higher levels of fighter!
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.
I'm still traumatized from the crit fail I rolled during a campaign five years ago.
I was playing a gunslinger, and made an admittedly foolish attempt to shoot a vermin crawling near my foot. I rolled a 1, and the DM ruled that meant I shot myself in the foot. I couldn't really argue with that outcome, but it was hard to come back from that. It was a harsh post-apocalyptic setting, which meant that the other characters were obliged to rib me for it incessantly, and my character could never seem to redeem himself afterwards.