Today's pensioners paid for older people of their day.
Also, you're only 25. You still have lots of time to increase your earnings, change jobs, get a promotion, meet someone to pool your finances with.
Older people don't have that time and are commonly in less good state of health, which further effects their ability to earn (plus there's the issue of employer age discrimination against older jobseekers).
Pensioners are on a fixed income and often have higher costs. For example lots of older people feel the cold more than younger people and are at home more, often less mobile, sometimes housebound. So that's extra heating costs. That's just one example of many.
Also today's pensioners mostly left school at 15 or 16 so started working 5 to 10 years before many of today's younger people. That's true to a large extent for Gen X too. They've paid their share, and also they do pay tax. VAT apart from anything else, and contribute to the economy by spending on essential and other goods (which helps keep businesses afloat and people in jobs).
However, as I've said, all in need should be supported. UK needs more social housing for all ages.