I think the question is different for the typical chess player compared to those at the very top. And at the very top we don't have that much data... going back to Fischer, he had a short career and disappeared by 32, but not really for lack of ability. For Karpov, his reign lasted about 10 years from age 24-34, but even after that he was in the top 3 or top 5 for another 15 years until he retired in his 50s. Kasparov reigned for 20 years, retiring at the top at age 41, and is maybe most impressive for defeating his same-generation rival Karpov while also holding the newcomers of Kramnik and Anand at bay. With Kasparov gone those two battled at the top for another 10ish years into their late 30s and mid-40s respectively (and I'd give the edge to the older Anand) before Magnus won the championship in 2013 and has been dominating for 13 years since. So to summarize, I don't think it's that "impressive" to still be winning at 35, he can probably keep winning for quite some time to come. He probably won't surpass his peak ELO though.