IR2 Visa and travel after reaching age 21

[nusratv]

My son got his immigrant visa recently under the IR2 category , unmarried child of US Citizen below age 21. The expiry date on the visa is 6 months from the date of issue of the visa and the expiry date is beyond the date my son will have reached 21. TO make it clear , visa issue date is 6th june, expiry is 5th December and he will turn 21 on August 7. My question is that does he have to enter before August 7 when he turns 21 or can he enter by the visa expiry date which is December 5.
Thanks in advance for any answers and feedback.

 

[Jackolantern]

He applied for the immigrant visa before turning 21, so the CSPA (Child Status Protection Act) will protect him even if he turns 21 before entering the US with the immigrant visa. He can enter the US at any time in the 6 months of its validity, whether it's before or after his 21st birthday.