Oh gosh, no 5 isn't too early. MOST kids start losing around age 5 or 6. Some even earlier at age 4. My daughter was VERY late eruption as a baby (didn't get her first tooth til 13 months). So because of that, she's also very very slow to lose them. She didn't lose her first one til the end of 2nd grade (so she was 8 years old). Even now at age 11, she's only lost 9. We're about to hit a period here soon where she'll lose several more.
I've had patients who are her age who have all of their adult teeth at this point though.
She's gonna be on of the unfortunate kids who will have braces in high school (anymore, a LOT of kids are out of braces in jr high, so graduating HS with braces is definitely not the norm). But she won't even be ready to have them until at least 9th-10th grade at this rate.