31 years, 251 days, 7 hours, 46 minutes, and 39 seconds to count to 1 billion.
To count to 1 billion would take 999,999,999 seconds, because the timer would start as soon as the person says "one", one second would
have passed when the person says "two," and so on.
Now, there are 31557600 seconds in one year
(seconds*minutes*hours*days). Divide 999,999,999 by that figure for the number of years. Then divide the remainder (which has to be less then a year) by the number of seconds in a day for the number of days.
If you keep doing this, eventually you get down to the number of minutes, and the remainder of that will give you the number of seconds.