It's alright, your English is great! And yeah, I used to level them up without thinking about their natures or EVs at all, but now I've learned more about them. I didn't really care about IVs, but now, I'm doing that, too. I transferred a lot of my level 100's to the newer generation, but I keep certain ones in my old games for memories.
I remember when I EV trained my first Gible in Pearl Version, and I realized that it had a lower attack stat then normal after evolving and training it to level 100. Then, I bred for another Gible to re-train. That's when I found my first shiny in one of my games ever, a Shinx. Its nature was actually pretty good (lonely), and so I EV trained it and leveled it up. I think I'll keep it in my Pearl game. Fun times!