It seems effort is more efficiently spent in changing perspective in ourselves and those around us, rather than trying to fight off inevitable old age and death.
By happy I do not mean the transitory kind of happiness we get from eating ice cream or watching a good movie, though that sort of happiness is important. What I mean is the stronger and longer lasting happiness we get from the confidence of being able to work through difficult circumstances instead of casting off the difficult circumstances.
This is because difficulty is inevitable in life, and we will feel happier looking toward the future if we know we can deal with difficulty instead of needing to avoid difficulty. So, knowing we can help people dealing with a difficult affliction like dementia means we can form relationships with less concern whether it will all turn out badly. Otherwise, we will instead tend to insulate ourselves from the perceived hardship, which will cut down our ability to form strong relationships, and strong relationships appear to be essential for human happiness.