Obviously if you have an illness or anything then there's little you can do.
But research is indicating that there are supplements (dhea is one) that can prolong life & quality of life. It does also depend on your diet, lifestyle & general health etc. So I would suggest that you research via google or yahoo asking questions like "what supplements can improve health" improve brain/mind function, what foods can do these things. Also there are on-line stores smart nutrition & synergy being a couple which sell supplements to help many things re improving quality of life.
Improving life quality can also increase life span - if you lose your memory you forget to eat, or take meds etc so die if your memory & mind stay fit you are more likely to stay fit & so liev longer.
Also there are machines like ces or sound/light machines (alpha-stim.Com or dynamind.Com) which help you relax, sleep better, reduce headaches, pain etc etc etc & so as you are less stressed you are less likely to get ill, have heart attacks etc & so live longer.