I am 26 and I play with tama's. Tama's came out when I was in high school and now they are popular again so its something new that I can still enjoy. My cousins are ages 7 and 10 and we play together, it is something that we can do together. I also think its important for adults to be able to relate to kids on a certain level, and kids will think its very cool if you can talk with them about things that they like, instead of the usual parent talk where parents just pretend to be interested but they really shun whatever their kid enjoys. They say things like, thats nice, and thats nice honey now go and play, instead of ACTUALLY talking to their kids and being actually interested in what they are, instead they just try to brush their kids off so they can get back to doing whatever they are doing. I think kids really enjoy when they find an adult who can actually talk about things that they are interested in, instead of just pretending to be interested in it.
I also don't think your ever too old for anything. In America we are way too hyped up on what is proper and mature for adults to do, and I think sometimes we just need to let that go. Besides its not like playing with Tama's is a BAD thing, you could be doing a lot worse things with your life than playing with Tama's, there is nothing wrong with playing with Tama's.