I’ve only met teens and young adults who care about such things...
Then you should get out more.
If you’re icked that you’re not the first person to be intimate with someone...
Ah, here's the basis for your previous remark. You are either intentionally twisting the argument or you have some kind of cultural bias showing. There's relatively few people who identify as men in the United States who care about "first" but there's quite a few people of any sex or gender who care about being the 50th.
...you need to ask yourself why the fuck does it matter?
Yes sex feels good but so does eating and many people will absolutely judge those who fall into gluttony because they will not restrain themselves.
...you need to ask yourself if it’s simply an issue with your ego and anxiety that the other person has had more or better experiences before than they have/will have with you.
Different things interest different people. Some people want an experienced partner who already knows that they're down for a three way on a balcony in Vegas because they've done it. Other people want a less experienced partner so they can experience the excitement of doing something that's new to both of them. I've had and enjoyed both kinds of partners.
And personally, nothing gives me the ick more than someone with a fragile ego.
For me it's judgy people who care too much about what other people think or do.