-Having to half-raise my sister, and seeing her be a selfish, spoiled, monstrous brat no matter how my parents tried to raise her--and utterly loathing any children I came in contact with. To this day, I refuse to hold babies when people hold them out to me. No thanks.
-Dealing with all the shitty comments of "you'll make a good mother someday"(when I cook) or "you'll make a good wife someday"(when I sew)--and having to remind them that men can do this too and I'll be oh-so-happy to teach any of my guy friends how to do it, while reiterating that I don't particularly want children but wouldn't mind marriage eventually.
-Knowing that the odds of my child being a bratty, obsessed with popularity whiner is something I couldn't deal with. I was always an outcast, and dealing with a kid who demands expensive clothes and a cellphone at age 7 is something I couldn't put up with. I -might- be able to deal with a child like myself, but again--someone like me would be treated like crap at school, be an outcast, and likely resent me for bringing them into this world just like I resent my parents for doing so. It'd be different if they were into books and stuff, but the odds of them being like that...are extremely low. I have a 99% chance of raising someone exactly like my sister, who gossips, whines, and habitually lies to get their way.
I actually don't know how old I was when I figured all this out--I know it was young, even at say, age 12 or so I wasn't into the idea of being a mommy someday. I had Barbies, but they would always go on adventures I copied from the books I read--they weren't moms, they were explorers and scientists.
I had someone once say that I have 'mom tendencies', but really those are just branded that way because they're "caring tendencies"--I show that I care about people. I ask them how their day was and I'll offer them a caring ear if they're feeling down, I tend to cook and knit and sew--which those are just things I like to do--I also like fixing computers and video games. I've taken care of drunk people before--again, not because I'm a 'future mom' but because I'm a good friend. I'm tired of caring and kindness being attributed to only females. It's highly misogynistic as well as misandrist.