Some meth addicts look 30 but are can actually be under 21. I would ask anyway. Who told you this? Management? F.E.? I can guarantee you when and if things go south, they will NOT vouch for you.
Card everyone who looks young-ish until you develop a sense for it. By then, you should be able to get a significantly better job.
Otherwise, if you work the desk, onsite fuel, or SCO, it's absolutely critical.
Not sure if you should ask for it? Ask for it. Unless someone is a schoolchild or freeman on the land, they need an id. And sometimes, even then.
Working here sucks. If you get stung, you probably won't get fired outright or even do jail-time.
But how many months or years will it take to pay off the fine? What is it worth NOT to go to court? What is it worth not to get hate glares and nightmare scheduling from management?
Having a first-degree misdemeanor might even interfere with getting a real job.
Besides, getting to find out a customer's real age is one of the only perks of working here.
If you get stung, neither the union nor management can help you.
The flipside is that if someone doesn't have an ID, management has to back you up (however ineffectively).