Long in the tooth
Definition 1 of 1
Pro Tip 1/3Often Humorous
The phrase is frequently used in a light-hearted or humorous way, rather than as a serious comment about someone's age. 
My dad is long in the tooth but he can still beat me in chess!
Pro Tip 2/3Informal Contexts
It's common in casual conversation among friends, but may be seen as impolite if used in formal situations or with strangers. 
We're all a bit long in the tooth for an all-nighter.
Pro Tip 3/3Not Literal
The phrase isn't about teeth. It's a metaphor for someone's experience or tenure often coinciding with older age. 
Professor Moore is long in the tooth, so he has a lot of wisdom to share.