Yes as long as the child is over 18 years old there's no problem. Great place to live.
Check the rules. My understanding is that residents have to be 55 or over. Of course family visiting for a short stay is ok. If he is living with you all the time, he would be a "resident" who doesn't meet the rules.
Realize most residents are over 55 years old. Please review: https://www.retirelasvegasstyle.com/sun_city_macdonald_ranch
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