As monkey nut said on the last page, if your solution is increasing birthrate you are basically advocating a pyramid scheme.
The current average life expectancy in the UK is 80. The retirement age will be 68 for most of the current population. So on average, pensioners will be subsidised for 12 years of their lives.
Compare this to a newborn child who will be heavily subsidized for the first 16 years of their life, and generously subsidized for a good years after that too (colleges, universities which still get a lot of money from the government despite the rise on fees, apprenticeships etc).
With that in mind let's compare the figures...
Government Money Spent On The Aged Annually
£74.2 bn - Pensions
£8.11 bn - Pension Credits
Total: £82.31 bn
Total Over 12 Years: £987.72 bn
Government Money Spent On The Young Anually
£56.27 bn - Dept For Education
£51.54 bn - Education funding agency
£46.42 bn - Schools
Total: £154.23 bn
Total Over 16 Years: £2467.68 bn
Source
* Of course there are other things I couldn't get like the age related breakdown of NHS spending (I can't see maternity and children's walls being cheap though), free bus passes & T.V Licenses (although they may be counted under the Pensions figure) and a few other minor things which are unlikely to change the picture you see above.
Solving the ageing population by producing more kids is like trying to solve a £10 debt by borrowing a further £20.
You missed health costs for ageing population which are huge, nearly everyone in hospital is over 60 and that's just me going to work looking at the ward day sheet and seeing that nearly everyday it's all over 60s and its not even a care of the elderly ward