Answer:
31 years and 3 months or non
Explanation:
the first thought that comes into my mind is
1 month=7 mice
n month= 7×n=2625 mice
n= 2625÷7=375
so it takes him to 375 months = 31 year and 3 months
but putting on a 2nd thought, I noticed that mice and mouse is different species. so there aren't exact answer