If an alien species ages a year every human month, how old would they be, in human years, by the time they're 2,000 in their species time?

Hey there!
If they're 2,000 in their time, then they must have went through 2,000 months given that they aged 1 year/month.
That means we're converting 2,000 months into years.
Because 12 months is a year, we divide 2,000 into groups of 12 (2,000/12)
to get 166 as our closest whole number. 12 times 166 is 1,992, so the remainder is 8 months.
Therefore, the aliens are 166 years and 8 months in human time.
Hope this helps!