Bert

Also Walloon: https://wa.wikipedia.org/wiki/Pitit_no_walon
https://wa.wikipedia.org/wiki/Li_ptit_Bert_(roman)

Bert is also used as a short form of Bertram.

In 2018, 52 is the most common age for an American (U.S.) Bert* who is registered male with the Social Security Administration. It is the 1, 533rd most common male first name for living U.S. citizens.

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*as a first name, not a nickname.