Being one squarely in the middle of the baby boomer generation I recall many from the generation before; those who actually lived through or fought in WWII, who could neither, or had trouble, reading and/or writing. Even though that may have been the case they were considered neither dumb, nor inarticulate in many cases. That, of course, is no excuse in this day and age for not learning proper spelling and grammar but I, for one, seem more forgiving of these deficiencies than many on these BBs, possibly because I remember these things.
So lets lighten up momentarily on the grammar even though it's now a necessary skill in a more competitive world.
It also seems odd to me that a young person is concerned about what adults think of him. As a kid I remember my dad, a WWII vet, always being proud of "hanging out" with the younger guys and I find myself relating better to younger people in real life than I do with those who are older. Of course there are limitations and there are exceptions but "hanging" with guys (or girls) half my age isn't uncommon. As a kid I didn't really think at all about what adults thought of me. I was a kid. I did kid stuff and had fun and watched adults that I admired and tried to be like them and that was about the extent of it.
All that said, my advice is don't worry about it, be a kid, but find adults you admire, watch what they do and how they act and interact and emulate them. The sooner you "act" like an adult the sooner you will be accepted for who you are.
