That's a gross generalization. Aging curves don't apply the same way to every player, and the best you can do is to say that certain types of hitters tend to age in certain ways. True talent level changes all the time with injury, skill changes, adjustments, etc.
Depending on how general you want to be, you can say that hitters tend to have a more gradual increase/decline as opposed to pitchers who tend to advance/decline rapidly and then plateau. The most general thing you could say is that most hitters gradually improve into their late 20's, then steadily decline.
If you want to get into specific skill sets, that's a whole other thing. For example there are hitters with "old player skills" (high walk rate and isolated power relative to age, lower batting average and speed). Those players tend to peak earlier and then decline earlier. Pat Burrell is a prototypical example. So you look at younger players who display those skills now (Chris Ianetta) and it might be a sign that he's not cut out for long-term success.
What you're talking about is nothing I've ever heard of. I'd imagine most players lose bat speed on some kind of aging curve as time goes on, but I've never heard of age 33 being some magical point where the decline is sharp.