There really is not an age limit, just make sure it's worth his time and money. The entire procedure is about 6 months long. If he smokes, the chance of success is less. Also they need to make sure he has enough bone to place the implant. If there is not enough place between the IA canal and crest then it cant be done. Thats not always the same for the maxillary sinus because sinus lifts can be performed. After the implant is placed, it needs to heal for at least 4 months, then place a healing abutement to establish a good sulcus around the implant, then the actual abutement and crown.