上年纪 is a separable verb (离合词) meaning 'to be getting on in years' or 'to be aged'. It is used to describe someone who is growing older, often as a polite euphemism for old age. The verb 上 and the noun 年纪 can be split to insert 了 (aspect), measure words like 点儿 or 几岁, or other modifiers — e.g., 上了年纪 ('having gotten old'), 上了一点年纪 ('a bit older'). It is commonly used in the predicate position with 了.