Speaking from experience...my wife and I are nearly 70 y.o. We have a 36 y.o. non-verbal autistic daughter. She functions on a 2-3 y.o. level. Your life will never be that of a traditional family or parent which is something you need to realize and accept as early as possible. Then you can move on with less stress and in a positive way. This doesn't mean it will be a bad life. For example, when my daughter was young we went to Disney, Universal, the beach, restaurants, etc.
The real kick in the teeth for us came when she was about 21 y.o. She started to get angry and aggressive. One time we had here in a buffet style restaurant. We were sitting in a booth. Behind us was a big, biker looking guy and his wife or girlfriend. The guy went to get their food, my wife went to get hers. My daughter was angry angry, I assume because she wasn't being fed yet. She reached around and went to grab the woman by the hair. I jumped across the table and grabbed her arm just in time to avoid a bad situation. We took her to the doctor, then to a psychiatrist who diagnosed her as bipolar. The bipolar is far more difficult to handle than the autism.
We haven't done any vacation trips or even simple things like eating in a restaurant for more than 15 years.
My daughter has been going to school since she was about 3 y.o. First she attended a specialty school for autistics. For the last 7-8 years she has been attending an adult program for mixed disabilities. She's doing well but we still deal with anger and aggression.
Being the parent of a severely disabled child or young adult can be isolating for obvious reasons. Also, there's very little, if any, spur-of-the-moment activities. Everything needs to be planned or simply not done. These things can be tough.
I was training at a children's hospital when my wife became pregnant with our first child. Children's hospitals are odd places because they tend to funnel the sickest children, the children with the most severe special needs, and the one in a million cases into a single healthcare facility. Working there day after day and being funneled these kids you quickly get a distorted view of reality and while you know the actual (and ever-changing) stats for things like autism spectrum disorder, in your day-to-day life +50% of all patients who entered the clinic had been diagnosed. As you know, these kids can be a challenge for parents, teachers, healthcare professionals, etc.
I'd say 1/4 to 1/3 of patients in private practice are "on the spectrum" and it is common to see kids who were previously manageable in an outpatient clinic setting become less or completely unmanageable with the onset of puberty. As they enter early adulthood they tend to either revert back to being manageable as we work with them or continue to down the path of being even more unmanageable. We typically take these adults to the OR. Obviously, new psychiatric diagnoses significantly add to the difficulties and challenges and bipolar disorder with its later-onset can really be a challenge. With this in mind, I was terrified for the birth and early part of life for all three of my children have witnessed the very real struggles that some kids/parents/families endure. While I certainly don't live with these struggles day-to-day, I do make my living having to navigate these issues on a daily basis.
We learned when my wife was pregnant with our 3rd child that she is a carrier for fragile-x syndrome. This is an x-linked disease that affects females much less than males. It is also the typical example in medical genetics courses for triple codon repeat diseases that show "anticipation". Basically, this disease is caused by repeating codons in a gene on the X-chromosome that inactivates the gene - the more repeats the more affected you are and it shows amplification of the repeats with every successive generation. For females, because they have two X-chromosomes (so one working copy of the gene) it can mean mild issues with memory and an increased risk of dementia later in life. For males, because they only have one copy of the x-chromosome and they receive it from their mother, it is the number one genetic cause of autism spectrum disorder and profound mental disability in males.
For all three of my boys, they had a 50:50 chance of receiving an affected x-chromosome from their mother - none are affected and none can be carriers. After early amino during the pregnancy of the third kid, we met with the genetic counselor and it was a short meeting. She said we had won the genetic lottery 3x in a row - stop reproducing. We scheduled a tubal ligation as part of my wife's c-section.