if being immortal is only awarded to those who can afford it (meds or something) then the person is going to lead a sad life later on.

all the fun / thrill in this world is around because of our simple and short life I believe. To do things and succeed under all its "life" restriction made all achievements all the better. Extreme sports for example would lose its charm if we are immortal. To being able to do something while putting your whole life at state is a bliss.

plus I doubt that it is fun to see everyone else around you die while you are the only one still living. If we feel that 5 years could be a short time, then an immortal would feel that 50 years is a short time. Before they know it, their child is replaced by grandchild, great grandchild, great great grandchild. Their friends gone, replace with their children and grandchildren too. Time will fly so fast that life would be dull and its only a matter of time before death is desired.