Part of the problem is that when your parents teach you bad habits or allow you to develop bad habits (my particular experience), it's not only hard to change them, but it's hard to realize that you need to change. Add in fatlogic, and it seems impossible.

My mom taught me laziness and to eat whatever I wanted. She was always thin, but I wasn't because of my genetics. When I was diagnosed with hypothyroidism, that explained my recent weight gain. When I kept gaining weight, the fact that my hypothyroidism wasn't fully controlled explained that. Throw in any other fatlogic and it just makes it harder to break free.

I'm not arguing that people take responsibility for their situation, I've taken full responsibility for mine and I'm fixing it, but it explains how I could let it get so bad before I did something to change it. Even now, having lost 85 pounds and feeling great, I struggle every day with the bad habits I learned as a child. They're my biggest source of stress and it's really hard. That's why I'm doing everything I can to teach my kids to eat reasonable portions, my second biggest source of stress (my oldest likes to overeat and is always complaining that she's hungry, which is hard to hear from your child).

It's not as easy as saying "this is the age it becomes a person's fault". And regardless, assigning blame does nothing anyway. I can blame my parents for me becoming morbidly obese or I can blame myself, but it doesn't change anything.