I wouldn't worry about it. Every study I've seen on the matter has clearly stated that it's a relatively small effect and is dwarfed by improved knowledge and experience. Overall intellectual performance is still rising at that point.
Those are IQ tests (mental quickness on tiny tasks), that don't cover knowledge and wisdom.
Is wisdom relevant to programming? 20 years of COBOL experience doesn't help much when writing Kotlin.
Experience of design patterns would seem to be most relevant to senior technical roles and program architecture... which is where you see older programmers.