I can't say that I'm whatever age that people would consider me to be to old and still like it, but I'm fourteen and will be fifteen in January and love everything about Pokémon. This entire franchise is the longest memory that I have with me, so I don't think I'll ever not like it.
The show came out in 1999, right? Well I was five and actually understood the concept and so, I kept watching it. I still remember the whole series, which surprises me since that's the only thing I can remember from my early childhood(I'm considered a teen now, right? *checks age - fourteen* yep, I'm fine). So if you're eight, eighteen, or seventy-eight, it doesn't really matter. I guess it just matters whether or not it's important to you.
N.E.V.E.R. Q.U.I.T. L.O.V.I.N.G. T.H.E. P.O.K.É.S.