Time: 1682ms

Golang version seems to be fine for me. You are not supposed to calculate the actual value of the factorial. Inputs go up to n=1000000000, and even with bigint, calculating it will take forever.

I am going to close this as not a kata issue, because my Golang solution which uses exactly the same approach I used in other languages passed.

Also,

strings.Split(s, " ") is equvalent to string.Fields(s)

I'd say the proper way is:

import "unicode/utf8"

utf8.RuneCountInString()

Seen this on Go blog.
Cheers :)