Yes, you certainly can begin an acting career at 20. Acting is a craft and a skill, just like any other job out there, so practice and experience are essential. You can obtain degrees in acting and theater; you can take in-person classes or studio classes.
Can I wear jeans to an audition?
You don’t need to dress like you’re going in for a corporate interview here. Your clothes shouldn’t be a wrinkled mess, but you also shouldn’t be wearing business attire to an audition. A good pair of jeans can go a long way, and it’s worth investing in a pair for auditions alone.