Experience matters?

I play since 2015. Training every day, always in good league positions. In this moment In a lvl 40 mánager Every season my players, even good ones turn to mediocre, and I must retrain then. Thats the game, I get it. Why, then, I've found players that started tus game 4 months ago and are at my level (or better)???

The starting date deosn't matter.
it's not real, just some things happened.
Started the game again after a long time, playing from a google account and then connect his team with a fb account, things like this.

If they've been away a while, when they come back, it resets the start date.