The NI fund isn't just for pensions and isn't ring-fenced in a way it perhaps should be.
The government pays nearly £100 billion a year in pensions - more if you count pension credit and housing benefit for the over 60s.
£27 billion wouldn't go very far. In any case, it doesn't make sense to have £27 billion sitting in a "pot" when higher interest rates are being paid on debt. Not paying down the debt just kicks the problem further down the line.
The amount the government pays has reduced slightly as the pension of 1950s women has been delayed, but it's due to increase massively as 1960s men and women reach pension age.
I don't think the pension age should be increased to 70 or 75 because most people over 63 have some kind of medical condition which makes work difficult. However, it's just sticking heads in the sand to think something doesn't need doing. Governments should have started doing more gradually decades ago, but they were too interested in votes.
I would like to see the value of state benefits increase to a living level for everybody, which would mean those over 60 who can't work could claim benefits until state pension age. However, that's a non-starter because people would start bleating about benefit scroungers.