I agree with Lostinbooks. Do what makes you comfortable.

I am 41 and don't dress the part. I wear graphic tees and jeans and I enjoy wearing odd colored nail polish. But then again, I don't concern myself with how others see me. Don't like it, don't look.

As for the issue with your parents, a good counselor can help you sort out why you are afraid to show physical evidence of your adulthood to your parents.
Without knowing a whole lot more about you, we can't possibly say why you feel the way you do.