Aging out while H-4 to F-1 COS pending

Hello Friends,

My son is a 3rd year student. Currently on H-4 visa. His I-94 is valid until Jun 30,2021. He will turn 21 on March, 11, So I applied H4 to F1 COS which is currently pending with USCIS. I got receipt number from USCIS. University said if he will not get approval before March they will issue a differed I-20. My question is.

Do I need to apply for bridge application (B-2) if I will not get approval by March 11 even his I-94 has date until June, 30 2021?

Can he continue stay while COS is pending?

Does it still consider if RFE comes after March 11 or he will be Out of Status?

Please help.