Double what?

Pre-ACA a non-group plan that wasn't some government mandated high risk pool would typically be much cheaper than group coverage, simply because of the fact that it went through underwriting and you could be denied.

It was priced similar to life insurance where a healthy young subscriber could get a very cheap premium because the expected value was so low.

Back when it was legal to charge 10x more for a 55yr olds plan than a 25yr old, people paid more in line with their expected utilization. Flattening the rate curve shifted massive costs to young middle class families, which IMO is shit policy. When you're 55 you are generally done raising the kids and saving for their college, so it's actually not a bad time for your health care premiums to skyrocket.

That wasn't my experience at all. Health insurance was literally three times more expensive for me throughout my perfectly healthy twenties compared to now as I'm nearing 40 (on an ACA plan).

If we are swapping anecdotes, my experience is the opposite of yours. I'm paying almost double what I paid 10 years ago, and my deductible is four times higher, with separate deductibles for drugs, and a smaller network of providers. Along with higher co-pays, and coinsurance now.

Double the monthly fee for an equivalent full HMO plan that was about the same as I was making when I was working for a Fortune 500. I now pay a little over 1/2 what I paid pre-ACA for an equivalent plan through the ACA marketplace in NY state.