For about 17 years (from in my mid twenties!) I was quite sure that it was inappropriate for me to show my arms, wear skirts above the knee, and so on -- all the "age appropriate" rules.
Then, when I was choosing my wedding dress in early 2007, and trying to find one with sleeves to be age appropriate, a single experience completely changed my thinking about these stupid rules. The young sales assistant and my younger sister persuaded me to try on a beautiful sleeveless wedding dress with a neckline that hit diagonally at the very edge of my shoulders -- sort of off the shoulders but not hanging down next to the shoulders. It was exquisite, but what about the lack of sleeves on a woman my age (43 at that time), I asked. Both my beautiful, stylish, ex-model sister and the young and beautiful sales assistant looked genuinely puzzled, and both of them insisted that I actually look at my arms, and that there was absolutely no reason to hide my arms.
When I looked at them from all angles with the multiple mirrors they had there, I realised that all that time I had been thinking I had to cover my arms to be age appropriate, it was completely mad. I had been severely limiting myself for nothing.
So now, I try to question any age-appropriateness-related rule I find myself thinking I should be sticking to. So many of the rules are actually completely arbitrary and not about covering ageing skin (which I would do if wearing a veil were in fashion but otherwise it's a bit tricky! It's my face where my age shows, as CocoLion said, though I certainly don't see it in her case!).
I would feel silly in some teenage fashion, but I do now occasionally buy something from the children's department (though it's as likely to be the boys' section as the girls') and my own children (early 20s girls) are, if anything, proud of me, and positively encourage me to wear shorts etc.
Moreover, I have seen catty comments ("mutton dressed as lamb") from people in their 20s and 30s on an internet forum about a woman in her 40s whose style seems perfectly fine to me (and not remotely MDAL), so if that stylish woman can't avoid the MDAL slapdown, well, I conclude that to avoid the MDAL accusation one would need to dress in a depressingly dull, great-granny-of-100-years-ago-like manner, and that wouldn't be me, so I'd then be falling foul of the "be yourself"/"be authentic"/"your dress should be congruent with your personality" rule. How about forgetting the silly rules and instead each person dress in ways that he or she enjoys and we all stop disapproving of others' style choices?
Sarah