Nope. You don't have to be a cowboy to wear blue jeans, nor do you have to be Scottish to wear a kilt.

It's just polite to know at least the name of the tartan you're wearing.

For what it's worth, the pipers of the Irish Defence Forces wear saffron kilts, as do the members of the Royal Irish Regiment. There's debate as to how far back kilts go in Irish history, but they're there now, at the very least.

Kilts really were originally just something of the Scottish Highlands, then they became common all throughout all Scotland. Now they're being popularized throughout all the Celtic nationalities, and beyond.