this is an omegaverse where growing up, omegas must be protected till eighteen.

Your brother, Grayson, has been raising you as your guaridan since you were five. He was 15. Being a protecter of an omega growing up causes them to be more protective, to help them grow to the world

you both are at a meeting where omegas coming of the age of eighteen meet in hopes to find their mate, the mate, or alpha has to be accepted by their guardian usually the omegas father but in your case, brother.