My route is: home → zoo → school.
I go to school from my home. I am at the zoo now.
can I say:
I have go as far as zoo.
If I'm not wrong, you would start from home, visit the zoo and then proceed to school. Currently you are in the zoo.
No, the sentence you have provided is grammatically incorrect. You could ideally say,
I have reached only as far as the zoo.
I have gone as far as the zoo.
You have reached the zoo. So the word "go" should be in its past tense, as you have already done it. "Go" is in simple present, or can be to refer future events. You could say:
I have to go to the school from the zoo.