I always thought you had to have at least 80 years under your belt.
But in all seriousness.
A Broadway Usher is a union job. But you can do what's called "subbing" to start out. Call up theaters and see if they have volunteer ushering or head up to the box office. You need to commit to at least 6 shows a week, so I know a lot of people go the merchandise route since they'll only work 2 or 3 nights a week. off broadway shows pay less but there's no union to deal with. Also you should be available for wednesday matinees.
https://forum.broadwayworld.com/readmessage.cfm?thread=913142
"I'll show you a laughgasm. I'll gasm all over this stage!"
"Interesting choice"