why doesn't 'go' work here? How would one say 'he is able to go' in danish?
Depends on the context. The broadest translation I can think of is "Han er i stand til at tage afsted."
So without contacts, go should be acceptable. Correct?
Can you use the phrase "i stand til" to denote ability in other situations too? For example: Han er i stand til at lave frugtkage.
Yes, as far as I understand. Not a native, though.
There's no necessary difference between "is able to" and simply "can", so both should be accepted.