Ask an Immigration Solicitor. Get an Answer ASAP.
I can help you for your concerns.
if he wants to visit in UK then you can sponsor him for visit visa.
if he wants to live in UK permanently.
you have explained that your son is 31 years old. He should look a job with such an employer which has licence to issue Certificate of sponsorship.
if he gets such job then he can apply Tier 2 visa.
he can apply Tier 1 investor visa or Tier 1 start up visa.
i hope it will help you
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