From Longman Dictionary of Contemporary Englishbe in your 20s/30s/40s etcbe in your 20s/30s/40s etcto be between the ages of 20 and 29,30 and 39 etc Matthews was already in his mid-40s. → in
Examples from the Corpus
be in your 20s/30s/40s etc• A black man, believed to be in his 30s, was shot after being confronted by police.• He may be in his 40s, but this guy still can rock Arizona.• My buyer can be in his 20s or 60s.• The man police are looking for is in his 20s, of Afro Carribean appearance and powerfully built.• Most of the victims were in their 20s and 30s, he said.• People who are in their 40s and 50s will like it also, because this is about two kids from their generation.• Diller assembled about 25 executives, most of whom were in their 20s and early 30s.• I am in my 30s and married, but I am beginning to think the young men are not always to blame. 