As ancient Ayurved text says
समदोष: समाग्निश्च समधातुमलक्रिय:।
who's 'Dosh', 'Dhatu', 'Mala', 'Agni',are in the state of equellibrium and has merry soul Indriyas and mind is considered as 'swastha' or healthy.
Taking this definition of health into consideration, world health organization has also described health as a state of completed physical ,mental, emotional spiritual & social well being & not marely an absence of disease.If you don't have any disease or inform it doesn't mean that you are healthy your bodily functions your body itself,your soul should be in a blissful state. And your social & economic productivity would decide whether you are actually healthy or not.
Why One should aim for health?
The answer is quite obvious.
'धर्मार्थकाममोक्षाणांम आसेग्यम मुलभुतमम'।
one's natural actions i.e way of living life is 'Dharm' physical material achievemental is 'Arth' , better next generation is 'kaam' and ultimate end of pair being free is moksh . So if you want to lead a fulfilled life by achieving these four 'Purusharthas'i.e. you want to grow in your career ,you want to earn money, you want family-love-realtionship , or you want to be free soul ... The basic for achieving all the things in life is health ! Without being healthy it is not possible to enjoy life itself.
That is why I always say that, "People who want to live their lives to the almost humanly possible experience,have to persue the journey of being healthy".