Is it unusual a 13 year old to have wisdom teeth?

Yes: It is normal for a 13 year old to have wisdom teeth. At the age of 13, they are still developing and usually not visible in the mouth.

Very early: What you may be seeing are late erupting 12 year molars. Ask your dentist to check, and x-ray if required, to determine which teeth are erupting. And has your child seen an orthodontist, especially if there are alignment irregularities?