You didn't do anything wrong. It sounds like you are a civil, classy, and considerate person who chooses to take the high road.

It could be the age, it could be the lack of assertiveness. But ultimately for bullies, it's about knowing they could "get away with it."

I don't know which of the below applies to you, but here are a couple of possibilities:

1. Vulnerability: If you report a bullying supervisor for harassment, you could lose your job, etc.

2. You are an amicable pereson who desires peace and harmony: The bullies know you wouldn't report, retaliate, or stick up for yourself for the sake of avoiding drama.

The bullies tend NOT to "pick on someone his own size." So sad.