AITAH for not liking my sister’s girlfriend? (age gap)

My younger sister (18) started dating a 24 year old during her freshman year of college. The GF had a long term boyfriend when they first became friends. All of a sudden, my sister shares with me that her and her GF are now dating. I don’t know the entire story of how they got together, but the whole situation seems odd because my sister now denies that the GF ever had a boyfriend. It just looks like my sister is a rebound in the whole situation.

The GF will occasionally stay over at our house but isn’t out going and make an effort to talk to my family. The whole vibe of the family is that they do not like the GF but will never admit it or say it out loud.

Since the GF is 24 and graduated college, it is unknown whether she has a job or not and her career ambitions are unclear. Obviously, I want the best for my sister and want her to be with someone that’s ambitious and hard working.

The GF is also older than me, which makes the situation odd given how young my sister is.

My sister also chooses the GF over hanging out with the family many times. It seems like she cannot balance having a gf and the rest of her life.

AMITAH for not liking the GF or supporting the relationship? Everyone in my sisters circle does not have a problem with the situation but I cannot get past some of these things.