Well, it is no wonder. People used to say that the physical prime is at ~27 years, but nowadays star players start playing week in week out at 17. You‘ll have to factor that in, so it is not outrageous to say that the physical prime is around 24-25.
That was the case for Messi (2012) and even Ronaldo (2010), who did not even play that regularly as a teenager.
From that point forward, players have to adjust their games to stay relevant. And this ofc is most relevant for forwards, because they heavily rely on pace. Messi became the best creator and free kick taker on the planet as he got older plus his dribbling did not rely exclusively on pace to begin with, so he remained a top 3 dribbler in the world up to his early 30s. Ronaldo became a poacher, playing closer to the box. A not so noble transition, but successful nonetheless.
Mbappe is facing the exact problem right now. If not now, definitely in 1-2 years. He won‘t get any younger or faster. He has to adapt his game if he wants to stay relevant and prove the people who claim he is an all-timer right. Which could be difficult because he is a shit free-kick tacker, an average creator and his dribbling heavily relies on pace (like young CR).
He‘s made poor decisions tbh. He should have joined Real in 2020 or 2021 at the latest. Real was relatively down at that moment and would be seen as a savior, plus he was still in his physical prime. Right now Madrid is without a doubt the most successful team of the last years and has many stars, so an aging Mbappe has to find a solution or rather Ancelloti/Perez have to find a solution for him.