CAN A 22 year old girl date a guy who's 17/18 years old?

CAN A 22 year old girl date a guy who's 17/18 years old? the girl looks really young for her age, even younger than the 17/18 year old guy and the 17/18 year old guy looks older. do you automatically assume it's just going to be for a fun and never serious? tell me your honest opinion. thanks
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