In my opinion, you are never too old to watch cartoons. Animated shows have been around for 50 years or so and have been targeted at adults for years (The Flintstones, anyone?) - but my favorites are the ones targeted toward kids but have tons of jokes and references only adults can appreciate. Which is either an attempt to smarten up kid's shows or a good excuse for adults to watch Nickelodeon long past their teens. Either way I'm still watching cartoons.
Unfortunately some of my favorite shows were prematurely canceled. (I spent way to much time deciding if "canceled" is spelled with one "l" or two. In the US it's one, in the UK it's two. Now you know.) We'll always have reruns of Bugs Bunny and DVDs of the entire Jetsons series but there are some shows that aren't on anymore that I really miss.
5. O'Grady
This is a little-known show that was on The N (Nickelodeon's teen/young adult programming) when I was in high school and starting college. It was about a group of high school kids that tried to go about class while dealing with The Weirdness - a phenomenon that would cause random odd things to happen each episode. Odd like people starting to act like cats or floating like they're full of helium. The animation was purposefully sort of bad but the characters were great. I used to watch episodes online but I don't know if you can even find them anymore.
4. Daria
I love this show way too much for my own good. I have the entire series on DVD and adore every minute of sarcasm and cynicism it comes with. As much as I love it I put it down at #4 on my list because I think it actually had a good life for a series - continuing it past 2002 probably would have ruined it. I'm actually surprised it lasted that far into the millennium without self-combusting.
*Fun Fact: they make a Daria voice for your Garmin or TomTom GPS! I need to look into this.
3. Angry Beavers
This show is arguably stupid but I loved it and couldn't stop watching it nonetheless. It's about two brother beavers who get kicked out of the house when their parents have another litter and try to make it on their own. They're sort of like the Odd Couple - one is smart and rational, the other is goofy and spontaneous. They like to watch scary movies and have a friend named Stump who is, naturally, a tree stump. My sister and I still quote the show from time to time. "LOOOK! I'm looooooking!" Stupid but awesome, as cartoons sometimes must be (case in point: Spongebob Squarepants).
2. The Powerpuff Girls
In my opinion, this is one of the cutest cartoons ever created ever. It's worth the double evers, it's that adorable. The Powerpuff Girls were three little girls created by mixing sugar, spice, everything nice, and Chemical X, which gave them superpowers. They have to save the city of Townsville from monsters and other gross things and have a direct line to the oblivious Mayor who knows not to call them after bedtime, since they are in pre-school, after all. How can child superheroes named Bubbles, Blossom and Buttercup not be adorable?
1. Foster's Home for Imaginary Friends
Out of all of the cartoons I've ever seen, this was by far the most creative. Madame Foster (the tiny old lady with the round glasses) opened a foster home for all the imaginary friends children had created and then grown out of. Friends included characters like Wilt, the one-armed basketball player, Eduardo the big purple fuzzy scaredy-cat, Cheese, the weird yellow toddler-like thing, and most importantly, Blooregard Q. Kazoo, known affectionately as Bloo, the friend of Mac (the little boy in the middle). They got into lots of trouble, went on lots of adventures and had to do their chores to keep the Foster Home going. This show was full of charm and wit, and was loved by viewers of all ages - it even received 7 Emmys!
Do you have a favorite cartoon? I'd love to hear about it!