Ok so if "needing to be level 1" is required, then how about this.
Pathfinder 1e uses point buy, and they have suggested point buy totals based on the kind of game you want to run. So have "low power" "high power" "godlike" point totals suggested.
Pathfinder also had three xp charts for how fast you want people to level- if you're running a high power game, players level faster than in a low power game. *For those people who use milestone leveling, it doesn't matter if you don't track xp, you would be leveling players faster or slower based on the kind of game you're running, this is just to show DM's what they can do to capture the feel of the game they want.
Then, if you're running a high power game, players start with a 10 hit point "kicker" at level 1. If godlike, 20 hit points.
You all start at level 1, but obviously, the difficulty of the game and how quickly you cruise past the early levels and get to the power level you want will vary.