Mom thinks I'm still 15

I'm almost 19, and I wanna dress like a 19 year old girl, tight clothes, low cut tops, I'm super comfy with my body so I wanna show it off. My mom however tries to dress me like I'm 15. I was trying on clothes one day shopping and when the girl helping us brought a revealing dress over my mom said "oh no she's only 18. I wanna dress my way, but she always guilts me so I won't buy it. I've started ignoring her but I feel a double standard, as she encourages my brother to express himself and where whatever he wants, where she is the exact opposite with me and I can never buy what I want, and most of the time it's my money!