Personally, I consider the cutoff point between Retro and Modern as being when the sixth generation (PS2, Xbox, Gamecube, Dreamcast) ended and the seventh (PS3, X360, Wii) began.
I guess I’m a bit weird in this regard, because I did grow up with sixth gen games (I never had a GBA, but I did dabble with GBA emulation at the time) and thus should probably also feel the same way you do, but I remained quite fond of them even as a lot of people moved on to newer consoles and no longer shared my interests. I guess I had an easier time labeling them as retro because it was easier to justify me still liking them as opposed to “being stuck behind the times” or “being too poor to afford the newer games/consoles” like people used to say to me.
Like… yeah, I was too poor to afford the newer stuff, but that wasn’t the ONLY reason I liked the older games. I just thought they were neat and had sentimental value to me.