Your writing style looks very young. I would’ve guessed that you were in high school, maybe on the earlier end.

If it’s friends online, you might want to focus on that. Proper capitalization and periods would help.

If it’s in real life, then you probably act or “feel” younger than you are. It could be something like not having “street smarts”.

How old are you? How tall are you? What is the timbre of your voice?

You type like a child. I was genuinely shocked to see in the comments that you’re a 21yo male. If this is how you talk to people who are closer to you, that might be the reason

Well, there’s not much to go on. We don’t know you, we don’t have any access to your friends, and you didn’t tell any story that might help us guesstimate what’s going on.

That being said, a lot of the time someone gets pegged as the “kid” of the group, it comes down to either their relative age, or their behavior.

Some people are just naturally more childlike. Not childish, though there can be overlap. The kind of folks that are bubbly, or energetically happy, or tend to have a certain naivete, that kind of thing. It comes off as younger to some people, so they’ll start treating that person as younger than they are.

But the other part is that sometimes even a year of age difference changes things when it comes to perceptions and group dynamics. You’re 21, so if they’re 22-25, it really can be enough of a gap to set you up in their heads as the “young” one.

That’s the stuff that tends to be common enough to fit without knowing more, or assuming anything about motivations.

Are you sure they are intending it in a diminutive sense and not a familiar or affectionate sense? Buddy is pretty common to call people you are being friendly with in American English at least. If you don’t like a nickname or term of endearment, you can tell your friends not to use it, but fair warning, friends of your age might just tease you about it instead of respecting your wishes.

I mean, just reading that question as one long run on sentence certainly didn’t make me think of you as an adult.

Also, might be a language thing, but buddy has almost no age connotations and is used pretty frequently across age groups.

Probably the autism.

Sorry to be the bearer of bad news, but you’re going to have to actually talk to your friends.

Depending on your level of discomfort, you can do it in a group setting, “Hey, how come you guys always use belittling language towards me, it hurts.”

Or, you can ask face to face, but that might be more stressful, or it might not, I cannot speak for you or your friends.

The fact that you posted this question without any context on how old you are really, what you look like, how you behave, may be a clue as to your maturity.