Can I intentionally overestimate someone's age while guessing it?
Aren't you worried that would offend them?
It's fun to offend people on purpose.
You shouldn't intentionally do things that offend other people. It's rude and serves no function. You need to be more considerate toward other people.
What's the big deal? I'm not hurting anyone.
You are sort of hurting others, because these people don't want to look older than they are. How would you feel if someone said something to you that they knew would offend you on purpose?