I was just working up to having a quick burst of self gratifying pedantry but Allan Conn has pre-empted me.

It is debatable whether the Gaels were aboriginal inhabitants of the British Isles. "Celtic" culture arose in what is now southern Germany in the first half of the first millenium BC, by which time the British Isles had already been occupied by human beings for several thousand years. Callanish and Stonehenge were already old. What happened to the pre-Celtic occupants is not recorded but I doubt if it was pleasant.

Be that as it may, the Gaels were certainly not the aboriginal inhabitants of Scotland. The Scots invaded Scotland from Ireland in the late 6th and early 7th centuries AD previously occupied by (probably amongst others) the Picts who were, as Allan says, from the P-Celtic language group* ie. Britons. They were subsumed and their language lost by th e10th century. At its height, the Kingdom of Northumbria extended up the eastern half of the lowlands to the Forth and the British Kingdom of Strathclyde took up the western half as far as the Clyde.

Haven't probed deeply but as far as I cam make out, Mc and Mac, meaning "son of" didn't emerge till the 12th century.

*Celtic is a language classification not a race.