The phrase "year olds" refers to people who are a specific age, typically children or young adults, and it indicates the group of individuals who are that many years old. Full definition
When I moved back into the master bedroom with the baby, I put our 3 and a half year old son in there as well. (sleeplady.com)
A son who has had emotional regulation difficulties since he was 9 months old and a 2 - and a half year old daughter who just wants to please all day long. (heightsfamilycounseling.com)