#!/usr/bin/python3

pop = { 0: 16000,
·······10: 14000,
·······20: 11000,
·······30:··9000,
·······40:··8000,
·······50:··7000,
·······60:··6000,
·······70:··4000,
·······80:··2000,
·······90:··1000}

year = 2020
while year <= 2100:
··total_pop = 0
··new_pop = {}
··for age in pop:
····total_pop += pop[age]
····if age < 90:
······new_pop[age + 10] = pop[age]
··pop = new_pop
··# Every couple in their 20s have 1 child
··pop[ 0] = pop[ 20] / 2
··# Not everybody makes it to 90
··pop[ 90] /= 2

··print("Year: %d, pop: %dM" % (year, total_pop))
··year += 10

Year: 2020, pop: 78000M
Year: 2030, pop: 83000M
Year: 2040, pop: 88000M
Year: 2050, pop: 86500M
Year: 2060, pop: 84000M
Year: 2070, pop: 78250M
Year: 2080, pop: 71750M
Year: 2090, pop: 62625M
Year: 2100, pop: 51125M