Potty training—I end up scolding accidents / by what age should this happen?

Not scolding accidents is the most important thing. Scolding can make a child hold it in or start to dislike the toilet. Say something like "Oops, it came out—that's okay," and praise what they did well. Don't rush about "by what age"—individual differences are large, so respect your child's pace (for example, once bladder development lets them go 2 hours or more between times).