Yes Kirk, It is scary, but the ental "slippage" has already begun.
In your 30's it's barely perceptable and very slow. In your 40's, the slippage really becomes perceptable. (and scary)
I just turned 50, and the mental (and physical)aging process has now really becme apparent.. literally month by month.
At this point in life, you actually begin to grok... life is short! Damn short !
BTW... If you want to have children, don't wait around too long. I waited until 36.. and now wish I'd had children at a younger age.
It could just be that you notice typos more-- I seem to make the same amount now that I used to, if old USENET posts are any indication; but I think I type more these days (IMing, blogging, web-comments, etc.) and I think I'm more likely to catch a typo, now. Plus I tended to spend more time editing usenet posts than I do anything else (save, of course, work-related memos and documents).
On the other hand, my fingers have habits, and while I learned to type by staring at the keyboard, I now type entirely using my finger-memory of the keyboard layout, meaning that I tend to make sound-typos because my thoughts while composing are basically a verbal narration in my head. (As opposed to people who are visually-inclined thinkers.) That and sometimes my hands get placed on the wrong key position and I don't notice right away.
I think most of my typos that slip through are a result of incomplete revisions to already-written text, because I get distracted by other bits of the text I'm revising.