18 year old and 26 year old?

My cousin turned 18 about 5 months ago and is currently dating a 26 year old my aunt isn't happy neither is my other cousin (her sister) I'm 15 so I wouldn't really know much about this but hes looking to become a neurosurgeon, hes rich and his dad owns a huge hospital, so its not as if he sits on his *** and plays video games all day like some of her others boyfriends, but an 8 year gap is a little too big to ignore, opinions?