Basically, things got bad in high school, and by the time things cleared up, I was a shell of a human and never took advantage of it. Eventually things got crap again and now I'm up shit creek once more.
I was socially and academically fine in middle school. I had plenty of friends, I did well in school, and I showed decent academic promise. I wasn't a super achiever but I was well read and I was technically minded. However, I was a year younger than everyone else in my class and I entered puberty late. When I went to my tiny high school with badly skewed sexual ratios (2/3rds male), I was physically and emotionally immature on a level that was almost stunning. While in my freshman year, I was a) diagnosed with depression and b) managed to end up in the 99th percentile for weight for my age. In high school, I stopped reading and started deriving all of my entertainment from the internet and video games. No hobbies, no exercise. College was the same.
It took me five years to graduate. By the time I got my degree, I was 265 pounds. I came back home and got what was supposed to be a "temporary" job for near minimum wage. It's been a few years. I'm still there. I took home about $14k last year, and I have $35k in student loans.
I'm 25 now. I'm still fat. I went from 265 to 225 in about four months but I gained the weight back in 2015 after one of my few friends committed suicide. I'm 5'9" on a good day. I keep up hygiene - I shower twice a day, apply deodorant, use reasonable amounts of hair product, and I floss and brush like it's my job. I still live with my parents. I get up at noon, I go to work at 1:30, I work 'til 10, get home at 10:30, shit around on the internet and play games with my remaining friends 'til 2 or so, and go to sleep and repeat. On my Sundays, I run a role-playing game for some of my friends and we sit around in my basement like we're 12 again.
Interests? There's the RPG thing, I guess. Otherwise it's video games and internet. I have a few vices I pretend are hobbies. I still read, but less every year. I learned a language in college and I've almost entirely forgotten it. I used to care about things like politics and history but now I'm in a weird nihilistic slump. In 2012 I followed the election on an obsessive level, but now I shut out almost all news.
I've watched my friends either get lives and wives or slowly succumb to the shitty inertia of our lives. If I don't lose my friends to careers or women, I lose them to drugs, suicide, or political extremism. If I was addicted to heroin, my life would be a pretty close American analogue to Trainspotting. Instead, some of my friends are, so I guess that's close enough.
In terms of barriers to success? I'm definitely the main one. I'm fat, I'm depressed, I'm shit with people, and self-esteem is a foreign concept. I've tried fixing the first two, but I've quite honestly reached a point where I don't think I'm going to be able fix the third one. The fourth one has proved hard to fix - I was raised to equate feelings of self-worth with narcissism.
I know I have mental illness - I've tried to treat it for about ten years. Medication, therapy, you name it. I used to have thoughts about suicide. Nowadays, I just lose myself in routine and zone out. A long time ago, I aspired to be a diplomat or to work in national security/intelligence. Now, I aspire to make enough money that I can live out of the house.