How young can you get hyperparathyroidism?

Any age. Rarely, babies are born with this condition or predisposed to this condition for different reasons.
Any Age But. Although it is not common in Pediatric age and among very young but this condition can happen at any age.
More unusual younger. It is unusual to have hyperparathyroidism at age 26. Familial inherited conditions such as men1 and fhh should be considered in younger patients (under 40). http://www.ncbi.nlm.nih.gov/pubmed/15490051.