Mom compares me to my older sister.

I honestly disgust that my mom keeps comparing me to my older sister, she's always boasting about things my older sister has accomplish and then tells me maybe I should be more like her. She told me I shouldn't have my ears pierced because my older sister didn't do it. She constantly reminding me that I'm not on the level my sister is. My self esteem is already at a low and she makes it worse by what she says. It makes me feel worthless. I can't voice how I feel because she'll say I'm being disrespectful. Maybe she's right also, I do have nothing going for me at the moment. Everytime I try to do better I get knocked back down, when that happens I remember my mom's words. Maybe it's too late for me, I'm 27 with nothing going on in my life but being a single mother.