There is no meaning to a long life if you are not happy. Time spent in misery is harder than death. Most old people feel that way especially those who are abandoned by their children or those who have their children around yet find themselves alone most of their time.
There are also some people who spend most of their life in misery not just when they are old their entire life. They either do not make efforts to change their lifestyle or simply pretend to be happy with whatever life has to offer.
And then there are some, who have a short life, who know they are going to die soon and yet they have no regrets. They spend whatever leftover time they have creating memories for others. If someone who knows they are going to die soon and yet can enjoy their life, then why is it so hard for us, who are not terminally ill, who have an almost perfect life, family, and people around them to life a happy life.
The key to life is to appreciate what you have. Even if it is not what you wanted, atleast you have something. Someone out there may not have even that. And before you realize that, your life will be over and you may end up spending all your life living in misery while you had the choice to live happily.