11, going on 12. I was a fairly normal kid still. I had known most of my friends since pre-school, had really good grades, and while I was a bit chubby, I was really active.
The summer between 6th & 7th grade, I was given the choice to move in with my mom or dad (lived with my maternal grandparents until then and saw my parents on rotating weekends). My dad was a strict, but fair man who had an alcohol problem, but kept it under control when I was around. My mom was a bit...promiscuous and was either busy working 60+ hours a week as a manager at a retail store, or out partying to unwind.
After mulling the choice over for a couple months, my mom essentially bribed me into moving in with her -- it was the worst choice I ever made. Because my mom was never home, I had very few boundaries. The situation was exacerbated by the fact I was constantly bullied at school. She moved us to a relatively close-knit beach community, and being the chubby, quiet, introverted outsider made it extraordinarily difficult to make friends and caused me to be bullied regularly. I stopped trying at school to the point I'd ditch most day and started playing video games and eating to excess -- so obviously I went from being the slightly chubby kid, to the fat kid, which just increased the teasing. I also picked up some other pretty bad habits (fortunately not drugs, smoking, or alcohol) which are still with me.
To make things worse, my dad went off the deep-end when I chose to live with my mom. I was never blamed for it, but I still feel responsible. Before I was given the choice, I hadn't realized my dad essentially had been preparing for years for me to move in with him. He purchased a nice 2br condo in a kid-friendly neighborhood (I had already made friends eventhough I only spent a couple weekends a month with him) within walking distance (<1 mile) of the school I'd go to, and he managed his schedule so he was at work by 5 in the morning and out by 3 in the afternoon and had every weekend off.
When I chose to live with my mom, he sold the condo, quit his job and started drinking to excess. He made some questionable decisions which led to him contracting a serious STD and injuring himself in a car accident (which was most likely alcohol related). He spent some time in a home because the medications he was given for his disease caused severe delirium, then immediately after that was sorted out (it took months) the state prosecuted him for tax evasion and he spent a few months in jail.
Since then, he hasn't held a real job, lives off SSDI, and spends most of his time drinking or smoking pot. We have an extraordinarily strained relationship and haven't talked in years.
While it's obviously impossible to tell, I still lie in bed at night thinking about how things would've turned out if I had chosen to live with him. It's hard to imagine things turning out worse.