I just bought an army green military knee length shirt dress in Spain and they are popular this season. I believe that the right style and cut is ageless. Go for it. I had an amazing cream and black printed stretch cotton shirt dress on a tall pear shaped size 12 client yesterday and she looked great.
My shirt dress is straight (not A-line) so I like to wear it with skinnies as a tunic, or as a dress with boots or flats. Don’t go too tight on this style of dress though. You don’t want the buttons to pop open when you sit.