Did we expect it to grow forever?
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Do you currently see jobs demanding 50+ years experience?
Even if we ignore the fact that most jobs won't require any more experience to do than they take now just because we live longer, longer periods of time won't seem as costly to us either. Right now 100+ years of experience is absurd because the only way they could ever have that much experienced is if they worked from the day they were born until the day they died, and even then they would need to live an exceptionally long life. If we lived to 200, you could start your career in your 30s, get those 100 years experience, and still have 70 years - an entire current lifetime - to reap the rewards afterwards.
Being more realistic, there is some finite amount of money you need to put away to live indefinitely off interest at any given level of comfort. Right now reaching that threshold in the 50ish healthy adult years we have is a difficult but achievable goal for most people. But with more time you can reach that threshold on a less aggressive trajectory and enjoy retirement for substantially longer (all while being healthier to boot).
As a thought experiment, if you want to imagine how you would feel about your doubled lifespan, consider your current lifespan doubled from some previous threshold. Would you prefer to live only 35 years on average with 50 being advanced old age? Sure there might be some benefits, perhaps some jobs might lessen their experience requirements, but would this be overall a more pleasant world with higher quality of life? We did not choose a 75-100 year lifespan to optimize human happiness, it is just the number we happened to wind up at as a result of a process that did not consider human happiness at all.