It's likely that many people who are alive today will be around to take advantage of future anti-aging treatments. So if you're young enough, you win the birth lottery. Hooray, indefinite life span is yours. Otherwise, you wither and die.
I look at it this way: the near-eternity that occurred before my birth didn't bother me. So I won't be bothered by the eternity that occurs after my death. I won't be around to contemplate it.
You can take this line of thinking to either of its natural conclusions: the morbid one or the "seize the day" one. I'm somewhere in the middle. I try to seize the day, but I'm a realist.
Some days I grab life by the nuts. Some days I count the beads.
I won't be bothered by the eternity that occurs after my death.
Would you mind if you died tomorrow? What about in a year? 10 years? 100? 1,000? If you had a choice in the matter, would you ever want to age and die? Would you condemn others to the same fate?
I want to be alive tomorrow. Tomorrow I will want to be alive the next day. And so on. So I want to be alive indefinitely. This may or may not be possible, but it doesn't change the fact that it is desirable.
Don't get me wrong; I wouldn't mind an eternal or greatly extended life. But seeing as how I will not be cognizant of my nonexistence upon my death, I don't think it's worth getting too hung up about. I am probably too old to make the cutoff for the singularity -- or whatever similar event might kick off the path to eternal or thousand-year lifespans. So I find that it's best to maintain a cautiously optimistic attitude about my mortality. I am not expecting immortality, but it would be nice.
Would you condemn others to the same fate?
I don't think that's a fair question, given that I haven't said anything of the sort. I would love for everyone to live as long as they could and prosper to whatever extent they could. I bear no animus to anyone who will win the birth lottery and be born into the age of 1,000-year lifespans. Similarly, I do not revel in the unfortunate fates of those who were born in the dark ages.
How is that not ridiculously unfair?