Why does society set p2do alert on men in his 30s dating 20 year old girls?

I know somebody had a relationship with a big age gap (guy was 34, girl was 20) and their friends family especially the girl's parents and friends kept saying he was such a p3dophile so they had to end their relationship. It seems like the current society is on EXTREME P3DO ALERT right now. I also hear people say a man in his 30s trying a date a 20 year old girl is mentally immature and abnormal...What do you guys think?