Why do you think your DC won't "cope" with a particular age group? That is an odd assumption about the behaviour of First year students - many of whom work very hard. And actually, a lot of "under 20s" as Second year students will be in private rentals and coping perfectly with bills etc, which you think your DC wouldn't be able to do. So they will be more competent than you think your own DC is - so don't make lazy assumptions about all undergrads.
It's the behaviour, not the age, that is the issue, I suspect.
The constructive (rather than prejudiced) thing to do is to look for a university that offers a "quiet" hall, or offers a choice of shared flat within the hall with other students who want a quiet flat. This is a pretty normal choice available, and your DC should ask about that at Open Days when talking to the Accommodation Office. Accommodation colleagues attend Open Days & will be used to this question. It's not an unusual ask - a lot of Muslim undergrads don't want to be in "party" or drinking flats/halls, for example.
If your DC is diagnosed with a specific cognitive/learning disability, they should note this on the UCAS form, and fully disclose to whichever university they attend. THey should make contact with the Disability services at that university, keep in touch with those services, as well as their Personal Tutor,. They should attend whatever personal tutorials are offered, as well as actively seek out extra-curricular support groups - often run by students with similar disabilities.
Your DC can research all these things on the websites of universities they're interested in. I would recommend your DC do all this, rather than you. The ability to be independent, and advocate for oneself is really important at university.