Cognition certainly declines with age at the population level. See e.g. https://pmc.ncbi.nlm.nih.gov/articles/PMC4906299/.

yes but he's 30 not 90, and knowledge and experience continues to accumulate through life, which can certainly compensate

	▲	DustinEchoes 2 hours ago \| parent [-]
		The decline starts in your early thirties, and those who are pushing their cognition to its limit are the first to notice.