Your figures are way off. Government spending is in billions, not millions. The biggest cost at around 176 billion is welfare, health is 164 billion, state pensions 98 billion and education 92 billion.
The figures aren't way off but auto correct must have changed it to m. State pension is approx 100b & housing benefit is 26b. Either way I'm not sure how more old people and less tax payers help fitting the bill.
The costs of supporting a typical 2 parent 2 child family who pay minimal tax with housing benefit, tax credits, family allowance, education, healthcare etc is obviously going to be way more than paying a measly £137.60 per week to a pensioner.
Surely it depends on the number of 2 parent 2 child families vs the number of pensioners. For one the birth rate is less than 2 & the average age of the population is already 40. Plus are 2 parent 2 child families who receive housing benefits & tax credits the actual norm for that demographic? And if you are going to include healthcare costs for families surely you need to allow for that in the cost of pensioners as opposed to just the cost of the state pension or do they not use healthcare?