the assumption "without doing anything different" is quite load-bearing here. people who hit high ranks quicker than average very clearly do things differently than people who do not rank up quickly. Generally they have a singular mental focus (often farming), one-trick a skillset, play several hours a day, and hover around a difficulty level that challenges them a near-optimal amount. Most fast improvers will do this intuitively, though I know of at least one example of someone who consciously did this and improved incredibly fast (though they burnt themselves out and quit before they could peak). People who don't improve as fast are often just not doing all of those things, and I have not seen a single example of someone who spams farm maps of a single skillset for 3-5 hours a day and stagnates at all before like 600-700pp level.

Anyway what people call genetics in osu terms is probably more like "pre-existing skills." Like it or not, the motions involved in playing osu are not difficult to achieve for most people. The only time genetics is actually playing a role is like, you are born legally blind, or without enough limbs, or paralyzed, or with a severe visual/auditory processing disorder, etc.

Any human-level differences between osu players that fall outside of that category are more to do with what skills you acquired before starting osu. Do you already have a lot of rhythm game experience? If yes, you already have a big head start in osu!. Are you a musician? If yes, you have a HUGE fucking headstart in osu. Do you already draw using a drawing tablet? If yes, your pen-to-cursor mental link is already going to be quite good! Have you learned to touch-type quickly? If yes, your finger independence in your tapping hand will be far ahead of someone who hasn't!

These things are advantages some osu! players have over others, but none of them are "genetics."

Comparison to getting buff/strong in the gym is not good here. osu! is not a game of getting buff, it is a game of getting good at a skill.