Is it normal my bf is two yrs younger than me?

I'm 26, he's 24. I don't feel like there's a generation gap between us and he's extremely mature and conscientious as he's studying to complete his master's and a straight A student.

My family keep telling me it's so crazy how I'm dating a kid and that I have to be careful because he's so much younger. They tell me he might not know things, tell me women normally date older men and that they'd rather see me with a 40 year old than a 24 year old. I tell them we have everything in common and that we are great together and they just tell me he probably views me as leader and that I am the responsible one because I'm much older.

My brother is three years younger than me and they always refer to him as a child because he's 23. They always say things like when you were his age, years ago when you were 23, etc.

When talking about my boyfriend to my brother, they'll say "he's your age. Can you believe she's dating someone your age? I never thought she'd go for a younger man, it doesn't seem right and is slightly disturbing."

Again, I'm 26 and my boyfriend is 24 while my brother is 23. Many people think I look 20 and that my boyfriend looks 25. He's tall, wears smart casual (suit/tie with jeans). He doesn't act or dress like a child so I don't know if it's normal for parents to say these things.