There is no upper age limit if a person is in good health. Lower age limit is very much dependent on the degree of hair loss. Generally speaking, it is unwise to consider hair transplant surgery if you’re under 25 years of age, at a very early stage of hair loss and have a family history of significant baldness. By undertaking surgery at these points you could end up having a patchy result as your hair continues to recede or fall out and run out of hair to chase the loss and keep a balanced look. You will very likely need to have further surgery to fill in any gaps but with uncertainty as to how much further hair loss will take place.