This is the key for both men and women - no one seems to get that dressing young makes your age obvious (40+ "surf bum" men in nightclubs look just as stupid) , while dressing in a timeless, classic style makes your age very hard to determine. You won't look 18, but you can stay "30-ish" for a very long time. ;)
Im 35ish and wear the same jeans and rock t-shirt style I have worn for 20 some years. Funny thing is I get carded for buying alcohol on a regular basis and my fiance' who is 8 years younger than myself never gets carded. which she can't figure out (I tell her its the white hair--she has albinism, makes her look older than she is, then I get smacked so I stopped saying it).
I think one can dress young and classy - it's the women who are trying to wear the exact brands the kids are wearing. Also, some gals CAN pull it off. My hairdresser is 48 - very attractive gal and dresses very young but she pulls it off - she looks great! Some people just can't do that. In fact, I saw a gal the other day - 30ish and she was wearing shorts - not walking shorts either. This lady should NEVER EVER wear shorts - she had huge trunk like legs - lower & upper and horrible cellulite. What can I say? Some people just don't have a mirror or never use it.