I do not believe this is true. Perhaps if you are an elite international-level competitor in your 20-30s or something. But otherwise, no. I consistently add several kg to my powerlifts each year for the past 5+ and I’m late middle age. I don’t see any signs of this changing, in fact the more I’ve trained the smarter I’ve gotten about things, so I have fewer injuries etc, so even more effective progress. Buts it’s a hugely tiny incremental grind to get this. Probably impatient people get dismayed and stop. Fortunately it appeals to my personality so I stick with it.