I feel your pain--or at least I used to. Now I look every minute of my 31 years.
The truth is, weight can make you appear older. On the other hand, the trade-offs are so painful in terms of daily living that I'm not sure it would be wise to regain the weight.
As far as appearing older goes, I have a few suggestions you've probably already thought of--facial hair, getting some sun, and of course "dressing older."
On an odd note: A friend's mother had a similar problem--she was the same age as her husband, but looked much, much younger. To keep him from looking like a dirty old man, she found some comb-in grey haircolor for herself. Just a little did the trick.
I hope some of this helps. If nothing else, take heart in knowing you'll be as old and broken-down looking as the rest of us soon enough.