If the pacemaker is the only concern, in other words he is not dealing with any other heart diseases such as a cardiomyopathy, he will have a normal life span. The pacemaker batteries last for years and before the batteries stop working, there are signs of that happening months before the pacemaker stops working. His doctor will have plenty of time to have the pacemaker battery replaced.
The pacemaker batteries( it is understood ) lasts for 5 to 8 years.Later on you may need to either replace the same or prefer a new device.