I do not believe that scientists should help people 'beat old age' unless they want it. Prolonging the life of someone with Alzheimer's, a chronic disease, or a disability doesn't seem sensible if they are suffering.
If I could choose the age at which I would want to die, it would be after my 110th birthday, so long as I was healthy enough to enjoy it. If I developed some kind of illness that was crippling in the 'younger years' of old age, then I would not want to live on suffering for too long.
I agree with the author that, "adding years to your life doesn't necessarily make it any fuller." You can die in your thirties and forties and still have lived a fulfilled life. If you do the things you love, take chances, spend time with your family, and most importantly have fun...then who would disagree you didn't fulfill the life you had?