Normal for 31 year old males to hang out with 20 year olds?

Just curious to how normal it is for 31 year old males to be hanging out with 20 to 22 year olds? is that weird, showing they are not growing up? (going both ways, hanging out with both females and males of that age group)
Normal for 31 year old males to hang out with 20 year olds?
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