At what age can I marry and keeps my Social Security Survivor benefit?

I've never worked all my life in more than decade and only worked for 90 days temporary, but couldn't keep up mentally with the works. No work history since then and I'm almost fifty. I was also born with Autism and high functioning adult with Autism.

autism makes more sense than intellectual disability based on your writing.  often people with autism just don't do good on tests.  If I had to guess, I would say your general IQ is closer to 80-90 (in the low average range) with higher skills in some areas and lower skills in others.  And since you were tested 40 years ago as a young child before much was known about autism the IQ test is probably very inaccurate.

at your age, it may be hard to get agencies to help, but there are programs to help people like you get jobs.  it sounds like you tried to just do a regular job with regular hours without any help.  You can find a job that you can do at your own pace and have a job coach with you until you can do it by yourself.  You can just work 2-4 half days if that is all you can manage at first.  If you get good at the job, you can ask for more hours.

I assume you are in the US?  Have you ever tried getting help from the state vocational rehab office?  There may even be programs specifically for adults with autism nowadays.

if you get Disabled Adult child....never.  You only keep the benefit if you marry another disabled adult child.

if you have a disability and got benefits based on having a disability, it is still disability...before it was dependent, now it is survivor

If you get social security because you were diagnosed with intellectual disability, with an IQ near 70, that doesn't mean you can't work at all.  People with an IQ of 60-70 typically can work.

if you can only work part time, you can still collect social security, but if you find you can work full time, you can get married and not worry about losing your benefit.

you can also pay that $25,000 in debt you owe by working part time to supplement your social security.

i would ask social security this question