If not all of these sentences correct Which one Is.
1 When I was at your age.
2 When I was as your age.
3 when I was the same age as you are.
But "When I was your age" is the most common of all, I would say.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
Thank you billmcd and barb_d for your help.