Guys, he may be 18 but he may also still live with his dad. And I can understand that level of respect.

As far as your dad goes, have you asked him why he feels you should only wear a kilt for special events? Once you know what is really holding him back then you will find your path to converting his stance much easier. Also, list the reasons you want to wear a kilt. Write them down and add reasons under each that would make a good argument for wearing them. That way when you do reopen the discussion you will be prepared.