This is not really a repair question. But here goes anyway.
I am considering buying a 1991 Acura Legend. The mileage is 335,000. My question is, is this high for a '91? And how much more can I expect to get out of this car if I buy it?
Really depends on how it was treated for the first 335,000 miles. It was probably treated pretty well considering it got that far. 335,000 is very high milege; average is 12,000-15,000/year so 225,000 would be towards the high end of what is normal.
It may run to 500,000 (Honda engines will go forever if you take care of them) if you pay to get it fixed when it needs it, but you should probably budget a few hundred each month for repairs if it is your only transportation. If you get it cheap (less than $500) it will most likely last you a few thousand miles at least and could be cheap, reliable transportation for a while.
Try to get a maintenance record on it as it will tell you what has been fixed so that you can start planning for repairs in the future.