I have been with Aetna (formerly Bupa) for over 10 years. Never put a claim in until this year. I had a hip surgery a year ago, two emergency claims, and surgery tomorrow, for a total of 1.3m bht. Aetna paid for 100% of all. There is always a bit of back and forth for surgeries, but so far they have come through.
Premiums do go up with age, but I was informed last time I renewed that premiums were based solely on age, and as long as you get in before 65 and always renew, you would never get kicked out.