People often relate the age of a person to both mental and physical conditions of that person during their lifetime with the average expected mental and physical condition of the human population for the same age. Maybe that's why just acting responsibly is not enough, we must quantify and regulate every step in our lives.
@_sam__ That's my technical answer. Air food water is needed for survival. Sleep clothing shelter -follow. I think it has to be the most important area to focus on because it makes all the other areas of life easier to conquer.
The philosophical answer varies from one person to another. For me, it'd be family. Everything else is a very long way further down the list. Whatever it is, make sure you have fun in the process and discover what your true mission is, and try to avoid hurting others