Age is a funny thing. Some aim to keep its passing under wraps, giving us adages like “You’re only as young as you feel” and “You’re only young once, but you can stay immature indefinitely.”

There are plenty of recent developments that could make me feel old. However, greeting me in the electronics section at Wal-Mart, were brand-new Teenage Mutant Ninja Turtles DVDs.

They weren’t the movies from the early 1990s. Instead, they were the first episodes of a new incarnation of the heroes in a half-shell, looking more adult in style than those of the late 1980s and early 1990s, with a more aggressive logo to match. (Think Cy before and after his overhaul a while back — the change is kind of like that.) Characters I had known were reinvented, and plots partially or entirely reused.

The changes are actually a return to the original comic book series by Kevin Eastman and Peter Laird. According to the frequently asked questions page on the official site (www.ninjaturtles.com), the villains we knew were created for the cartoon, and so not on the new series — and April O’Neil isn’t a reporter anymore, either.

My time as marketing target was far in the past, so they have started with a whole new group of kids.

If the Ninja Turtles were the only example, it wouldn’t be so bad. But there are other things making me feel my age:

* ABC is recycling the “TGIF” slogan, last seen in the mid-1990s.

* Google is celebrating its fifth anniversary; I remember when AltaVista ruled the Internet search engine world.

* After costing 50 cents for … well, forever, it seems that candy bar prices reached a breaking point. Concession stands in Sheffield, Hubbard and Traer all pasted a big “$.75” on their price lists this fall. Vending machines here on campus have done the same. Remember the days when two for a dollar was the going price instead of the sale?

* Then there’s the “trucker” hats — or, for some of us, farmer hats.

Rather than seeing them on big rig drivers, we would more often see these mesh caps perched on Dad’s head as he did his daily work. Ashton Kutcher, himself an Iowa boy, popularized the “trend” enough that the mainstream media picked up on it — and thus Rolling Stone is declaring the fad dead in its Oct. 2 issue. Well, it may be dead to the coasts, but I’m sure farmers and truckers will continue to wear them, just as they have for the past 30 years. Even if he has a dozen (or two), the true farmer will never turn a new cap down, even when others won’t be caught dead in them.

Those hats aren’t the only things from the 1980s coming back. As the Daily itself reported Monday, in “Reagan-era fashions, music back in style,” some of the fashions on the market today are very similar to those we would find in high school yearbooks issued just as we began school (or just before — there’s me showing my age again). Instead of “The 1980s are over; let us never speak of them again,” as it was in the late 1990s, everything made fun of then has come, ahem, back to the future. I suspect the flashy neons of the early ’90s are going to be popping up any day now. Let us hope the Macarena won’t follow them.

In the past few years, Beloit College in Wisconsin has issued a kind of age barometer about incoming college freshmen, called a “Mindset List.” Issuing it on the basis that most freshmen were born in 1985 (and deciding to ignore the substantial percentage born in late 1984), this year’s list included such items as “Gas has always been unleaded” and “Stores have always had scanners at the checkout.”

Despite making an overgeneralization or two — for example, saying “They have never been able to find the ‘return’ key” when that key is on every Apple II and Macintosh keyboard — it’s largely accurate.

This list is something of an age-stopper for me because the second segment of the list still includes things I know, such as knowing who the “heroes in a half-shell” are (see above).

In the great scheme of things, measuring your age by how many times something from your lifetime is recycled is not exactly a reliable or even useful beacon. To really feel old, I just need to remind myself that my former neighbor and classmate is married, and two others from my high school class, including a close friend, are engaged. Given a choice between the two schools of thought, comparing the new Turtles to the old is just a lighter response to the passing of time. I will have enough time later to contemplate the heavier ones.