Normal is average

Normal is usually "average, plus or minus 33% or 45%" - i.e. the "middle 2/3rds" or the "middle 95%." Sometimes it's the "middle 99%" or more even.

Since 90-95% of people aren't gay, people with a "narrow" definition of normal can feel comfortable calling gays abnormal. Since well over 95% and probably over 99% of people over 25 don't have sex with people under 15, and well over 95% probably well over 99% of adults don't have sex with people under 12, society is comfortable calling that abnormal behavior.

Lots of things are abnormal but not bad:

Having a 150 IQ.
Being elected to high public office.
Being a billionaire.
On a worldwide basis, having an income over the US poverty level.