"My parents (and all of us probably) have paid for their pensions. They paid for it every year in National Insurance. It's not their fault (or anyone but politicians) that the money was spent the minute it started coming in and there is none left now"
They weren't paying for their pensions, they were paying for the pensions of the set of pensioners that lived at that time.
There pensions will be paid for by us, and our pensions by our children.
That's how NI works and how it has always worked, it's never been a pot of savings that people paid into.
However the system went more than a bit wrong.
People started living longer, so the cost of the system went up. And then people started having less children, so the money going into the system went down.
Rather than having a nice population pyramid where the old are supported by there being more young people under them we have what looks like an age apple. There are currently few old people, few young people and a big bulge of middle aged people, the baby boomers. When that big bulge hits pension age, and it has already begun, there will be trouble.
So the baby boomers benefited by having few old people to support when they were paying NI and by having us support them. When it's our turn to claim the system will probably have collapsed, we'll have "paid in" but get nothing.
It's not their fault and it wasn't deliberate but the baby boomers do have it good, or comparatively good to how the next generation is going to have it.