From Longman Dictionary of Contemporary Englishlong in the toothlong in the toothinformalOLD/NOT YOUNG too old – used humorously I’m getting a bit long in the tooth for this sort of thing. → long
Examples from the Corpus
long in the tooth• Some of our vehicles are getting a bit long in the tooth.• A real character, but getting a bit long in the tooth.• Although they were solid and durable, the old machines were getting a bit long in the tooth.• DataEase is a worthy contender, although it's a bit long in the tooth.• It's worth the extra money Hewlett-Packard's DeskJet 840C looks, if anything, a little long in the tooth. 