"be real" for being realistic, asking a better question that is not nonsense.

Loosely translated: "yo be real" = "Hey, please be more realistic with your future questions"

Ah sorry I thought it was some technical thing!

"be real" when spoken by humans means "be yourself" not "be realistic".

Depends on the context. But without context I’d read it as “be honest” or “tell the truth” first. So in the context of answering a question it pretty clearly means “ask a question I can realistically answer”.

Out of curiosity how old are you?

It's an Americanism.

ebonics https://www.youtube.com/watch?v=RrZlWw8Di10