Right age for marriage

My mom has been hounding me about wanting to get married lately. I have always thought I would wait years to get married that is until I met my SO. Now we are planning on getting married sooner but my mom keeps saying I’m too young. I’m 20 I’ll be 21 in September and he’s 19 and will turn 20 in July. She says I need to wait until I’m 25 because she married young and it didn’t turn out right. I think she’s just putting all the left over hard feelings from her ex husband on mine and my SOs relationship and it’s not fair. She’s also said that if I get pregnant right now she would be mad but when my sister was my age she got pregnant and my mom was ecstatic I feel it’s unfair like hat do y’all think