Whether by design or evolution, it seems it is the responsibility of the child to grow and learn, of the young adult to create, build or raise new young, and of the old adult to apply their wisdom to ensure the survival of the group.
The pursuit of happiness for its own sake does not fit into the plan.
Happiness will come from properly growing and learning, from creating and building that which is best for the group, and from doing what one can to ensure we don’t get totally obliterated.
Let’s ensure that the old can continue to contribute to the survival of everyone by never marginalizing them or underestimating their worth.
And in return, the old have to understand that they have a responsibility to ensure that civilization continues, even if that just means giving the young adults a piece of their mind now and then.