Gaelic arrived in Scotland within 100 years of English arriving in England. They are both attested to arrive in around the 4th - 5th AD century IIRC. Before that Scotland spoke Pictish (which is not known in the modern era and may/maynot have been a Brythonic language) and a language related to Welsh in the Lowlands. Gaelic is a very interesting language and should absolutely get championed and preserved, but it is not the ancient language of Scotland, and hasn't really been spoken there much longer than the English language was in the UK.