Should I Enter the US before i turn 21?

[Jeffin Matthew Jose]

I am the accompanying applicant.I will turn 21 on February 27th 2016,my visa had already been approved and passport is returned from the consulate.The Visa is valid till June 29th 2016.My question is whether I should enter the United States of America before I turn 21 or before the expiration of my visa and that is on June 29th 2016.
Thank You
Jeffin Jose Mathew.