"I think the chorus is saying
"Young Munro bi Charlie agam" ... the word 'agam' (pronounced 'AK-um') in Scottish Gàidhlig means "my," and 'bi' (pronounced 'BEE') is the imperative for "be". So therefore, "Young Munro be my Charlie."

This is according to a friend who knows far more Gaelic than I ever will.