Why do parents blame their oldest for everything?

Because the oldest should know better.

I'm not quite the oldest, but my big brother doesn't like being around the family sim basically considered the eldest when I'm around my two little brothers. I also am ALWAYS blamed for thing that I didn't even do, I often am also the one blamed when my brothers are the ones that do things to ME! I mean, honestly mum, what did I do? How am I to blame? I really do understand where you are coming form and I too hate it. My mum always says 'You're the oldest, you should know better than that' or 'Get some common sense, you shouldn't acted so immature'. I honestly think that my mum loves my younger siblings more than she does me and enjoys wrapping them in cotton wool. But soon enough I'm will be old enough to miss out of family stuff and not have to spend time with my younger siblings so I can't be blamed anymore.

Instead of getting defensive, talk to your mom (tomorrow, when emotions have calmed down) about how that makes you feel.

Instead of yelling things like, "You ALWAYS blame me for EVERYTHING and it's NOT FAIR!!", use statements in a quiet, calm voice like, "Mom, I know you get frustrated and sometimes it's very overwhelming, but it really hurts me when you automatically think I am doing something wrong without listening first to what happened. It makes me think you just think I'm a terrible kid who can't do anything right. I'm getting older and I need you to support me and be my cheerleader. I will try my best to own up to it when I really do make a mistake, I think I am old enough and responsible enough to do that. But I also need you to not assume I am doing something stupid every time there is a problem. I feel like it's pushing us apart and I don't want that, I want to feel close to you. I may be bigger but I still need to feel like my mom loves me and supports me."

Also, approach her when she's alone, and things are quiet and relaxed - don't bring something like this up when she's trying to cook dinner or get the other kids into bed, etc. Choose your timing wisely when your mom is not already stressed out.

Trust me - I'm a mom - if my kid came to me using phrases like that and in a loving manner, they would have my attention.

Because they hold the oldest ones responsible for everything.

I'm the oldest and I think it is because we should "know better" and it is easier for the parents to pick on us, that way they don't feel as guilty! Lol

constantly suck up to your parents so when your sister acts like a retard, your parents will be confused, also, act nice to your sister in front of your parents so they will begin to think that your sis is actually doing it wrong.

Old habit.

No