I am using condoms, but my brother, who is a year older, doesn't

So what is your question? Are you asking if that's normal ?

That's his personal choice.  It's awesome you're doing what you can to prevent pregnancy and reduce the risk of an STI.

You could calmly discuss this with him and maybe he could why he's not using condoms.  Yet, on the flip side, it may do more harm than good.