That's not 100% true.
Speaking as a guy, and from what I know about other guys.
* When we're young boys (say 13) see any hole, animal mineral or vegetable, as a potential partner. "Ohh look a vaccuum cleaner / knot in a tree / slightly curved rock / good god a GIRL!"
* When we get a tad older (say 15) we loose the mineral and vegetble bits, and start to focus on any girl or our hands.
* By the time were 18, we'll have developed some "preferences", but it still tends to be pretty flexible.
* By say 25, whilst you will have distinct preferences, say an age preference, there's certainly flexibility and examples still break it.
Give you an example. I'm 29, but I have no shame in saying that I still find Meryl Streep good looking, and for that matter Jane Seymor. (I have a long term girlfriend). A good friend of mine is 27 and he has a wife and kid, but on his 'safe' list is Sharon Stone.
The funny thing is, 33 just isn't "old" anyway. When I was a teenager one of the hottest women was Diane Lane. When I saw Judge Dredd I thought she was sex on legs. She was 30 (I think) at the time.
This is a good thing for you. If your 33 and attracting comments from 23yr olds, it's not the "milf" crowd your getting... it's the "damn she's hot wonder if I can bed her" crowd.