1
general::
Phrase(s): long in the tooth
Fig. old. • That actor is getting a little long in the tooth to play the romantic lead. • I may be long in the tooth, but I’m not stupid.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Getting on in years, old, as in Aunt Aggie's a little long in the tooth to be helping us move. This expression alludes to a horse's gums receding with age and making the teeth appear longer. [Mid-1800s]
American Heritage Idioms