Past it
Definition 1 of 1
Pro Tip 1/3Age Related
Often used to suggest someone is too old for a specific task or role. 
At 65, he's past it for heavy lifting jobs.
Pro Tip 2/3Colloquial Use
It's informal and might be considered rude or insensitive in formal or polite settings. 
I wouldn't say he's past it at the office meeting.
Pro Tip 3/3Not Just Age
Can also suggest someone's skills or relevance are declining, not solely their physical ability. 
The professor isn't past it; she's still brilliant.