the first question is whether you can claim him as a dependent even if you don't do so. if the answer is yes, then he can't have his own HSA. if the answer is no such as being 24 or over at year end (he fails qualifying child test) and not be a qualifying relative meaning his gross income for 2025 is $5200 or more or he provides over 1/2 his support
if you can't claim him as a dependent then yes he can have his own HSA see this interesting link.
https://americanfidelity.com/blog/reimburse/hsa-mistakes-dependents
also, note the family limit for 2025 is $8550
