What would be the correct Bar Mitzvah date in 1961 #general

Jx. Gx.

Can someone please tell me what would be the correct bar mitzvah date for a cousin who was born on August 17, 1948 or point me to a website that can calculate the correct date?  I have two likely dates, but I'm not sure which is the correct one: July 22 or July 29, 1961.  Thank you.

Jeffrey Gee

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