While I was re-watching a Friends episode (S6E21), I stumbled the line as below.
Why can't you get a girlfriend your own age?
I can understand what he meant (a girlfriend from your own age group), but I thought I wouldn't be able to use this kind of expression because I'm not sure it's even a correct expression.
To be specific, if I were to express in this way, I would probably try to come up with a proper preposition to place before "your own age", like "from" preceding "your own age group". Why is this usage okay and is there any underlying grammar?