Question about bearded dragon

Reno NV

Description

I have a bearded dragon I got from someone on here about a year ago and he told me she was one but she isn’t active she barley eats and drinks water she sleeps literally all day and night I wouldn’t cared if she was older but now it just seem like I’m having a dying beardie when she sleeps it don’t look like she’s breathing till I have too look at her veryy carefully just to make sure she’s still alive. So my question is how would I know how old she really is?