It might be that he's worried other people will give you a hard time for wearing it or that you'll get into trouble from the staff.

Perhaps sit down and talk with him and explain that you want to be sensible and mature about your kilting, arrange with him certain dates when you'll wear a kilt. Like Burn's night, tartan day and St. Andrew's day.
Or every Friday. Something like that.

He might get used to you wearing the kilt and be a little easier about it.