There are 31,536,000 seconds in a year, so if you spend a thousand dollars per second, you would be spending 31, 536,000,000 dollars per year. So, if I divide a trillion by 31,536,000,000 the result is 31.7 years.
No. The term "twelve year old" is a noun (someone who is 12). It can be an adjective, but should be hyphenated, as in twelve-year-old cat. *The Chicago Manual of Style suggests that both nouns and adjectives should be hyphenated. Other styles may differ.