The years are passing quickly, absolutely. But Mbappe knows that, he is aware that losing another season at PSG can cost him a lot in terms of his achievements as an individual player. I think it is already sad that he wasted a couple of years at PSG. It was entertaining in the beginning when it was Messi, Mbappe and Neymar, but retrospectively it didn't help him much except for becoming rich. But he would have become rich in any other club as well. Now he is in his mid 20s already and time is running. He could have broken dozens of records, but that is becoming more difficult now.
But it is becoming clearer every day that clubs will not want to sign the French attacker this season. Mbappe has made it clear that he doesn't intend to renew his contract with PSG, which means he will be a free agent at the end of this season. This will make him cheaper for clubs to sign him. Real Madrid was willing to get him this season but the financial implication plus his £893,000 weekly wage looks like a barrier.
There is not also any certainty that he would win trophies if he moves to Real Madrid or another English team that needs his service. PSG's new coach Luis Enrique shouldn't be underestimated, he is also making plans to make the club a force in Europe. He is targeting to bring in Joao Felix from Chelsea and Bernardo Silva from Manchester City.
You are basically right about this that Mbappe becomes cheaper as a free agent under normal circumstances, but nothing is normal when it is about Mbappe. He now wants the money that he would have earned from playing for PSG next season to be put on top of whatever he receives for a transfer from PSG to another club this season. Either the sheikhs are willing to pay him some form of compensation or the new club has to put the money on top. In poker you call that Mbappe move "ALL-IN". he isn't making a step back, he wants it all and I hope that even he has to realize at some point that enough is enough but my expectation is that he will get whatever he wants.