0-16 year olds = 31% (139,810,000)
16-45 year olds = 60% (270,600,000)
45-80 year olds = 9% (40,590,000)
This describes a very accurate Developing Country that had a baby boom about forty years (around the time of Dharma War I & II) like Unibot and doesn't put a lot of money towards seniors.
How did I do the calculations?
Population multiplied by ((percent of budget for defense X 1.5) / 100)= 16-45 year olds
Population multiplied by (Percent of budget for Medical / 100) = 45-80 year olds
Population - ((percent of budget for defense X 1.5) + (Percent of budget for Medical / 100)) = 0-16 year olds
I think my nation's life expectancy would be like 62, but I'm not totally sure on the formula. Also take a look at The Declaration for War rules page, theres a neat war stats formula I did there, If you liked this one.