Ah, programmers. I love how we can show the logic behind 3 correct ages for Bill when he wrote this :)
Then we can don our statistical machine learning hat and make an ensemble model out of the three sub-models.
Unless we do something exotic we're probably going to predict 25 as the point estimate of {24, 25, 26}.
Don't forget that approx 1% of coders are running on an OS with a bug in the DST times around that time frame. That makes his estimated age as 24 years, 364 days, 23 hours and 57 minutes.
However, since only one age value can be actually correct in this case, the use of logic looks less like a feature of the programmer's mind and more like a bug.
All three results are close to each other and to the true value, so I'd still call it a feature :).
One of them is a case of GIGO, using "36 years ago" as input when the correct value is 35. Fixing that reduces it to two values, and the discrepancy is down to day versus year granularity.
The reasoning behind two of those answers has resolution of one year, while the third one uses day precision; it seems that all three are correct within their error ranges.
He was born on October 28, 1955. Therefore, in August 1981, when the game was released, he was 25.
Current Bill Gates age: 60.
This little game was written 36 years ago.
60 - 36 = 24 <- Bill Gates age when he wrote this.
The game was released in 1981, so Gates was 26 years old.