What age can you tell if a puppy has hereditary health problems?

It is possible to to diagnose hereditary issues at almost any age, depending on the breed, type of health issues that breed is prone to and the age at which those specific issues are known to surface in the breed... Typically though, the most common health issues, such as hip dysplasia in larger breeds, don't surface until after maturity, around 2 years of age... Hope this helps!!!!!!