"Account age" refers to how long someone has been using or owning a specific account or membership. It indicates the duration of time since the account was created or registered. Full definition
The net effect was to bring down the average account age of my credit, and my score dropped along with it — by 30 to 40 points. (valuepenguin.com)
They should also take into account the age of the child and where they are at developmentally. (attachmentparenting.org)
If you're buying ahead for the Spring or Summer time, make sure to take into account the age of the child and how they might have grown by then. (thefashionablehousewife.com)