One(Non-Leap) Year in seconds would be
Secs per min X Mins per hour X Hours per day X Days per year
ie (60 x 60 X 24) X 365
equals 31536000
So 1.2 billion seconds divided by seconds per year gives us
1200000000
31536000
which is 38.05 or rounding down 38 years
Note your starting age is not relevant
