Disability Benefits: Child SSI

Hi Im in massachusetts My son is 20 yrs old disabled has never worked and collects 145.00 under disabled mom 100.00 of which goes to insurance taken directly from payment check, leaving 45.00 for medication and doctor visits.
Is it when he reaches 22yrs. old he will need to reapply for disability to be able to get an amount suitable to care for his own expenses if so how will that amount be determined.. Thanks

Disability Benefits: Child SSI