The entire model is predicated on not paying in each year exactly how much you take out in benefits. That would completely defeat the purpose. So, of course young people pay more than they take out, while they are young. Almost all of those young people will also eventually get sick, hopefully old, and need health care for many years in excess of the amount they are paying in that year.
Are younger people actually subsidizing older people over the long-run, in other words, are younger people today on a track to pay in more than their expected lifetime cost? I doubt it, I think that would only happen if a future event dramatically cut the cost of care, you could end up having over-paid if care became abundant and cheap.
Another way to think about health insurance premiums is, you are born, you start $300,000 in debt. That's about the amount of healthcare you're going to consume, and you have your lifetime to pay it off. But that "debt" is also growing at ~5% based on increasing cost and complexity of available therapy, and average number of therapies someone can survive. The average 25 year old should have paid for about 30% but may have only actually spent 10% of their healthcare budget so far, but you can rest assured the balance will eventually be spent. Doesn't mean they are being ripped off by the old people!