I say it depends on budget and how long you plan to keep it. Miles aren't the absolute indicator, but they're definitely a sign of wear on things you're not going to replace easily. First one I bought was '89 and 19k mi. Low for a 20yr old machine, but sitting is aging, as with anything mechanical. 20k miles later, that one needed a top-end, was pretty spent overall but it was trying to keep up with ktm's much of it's life.
The up-side with them is, upgrades can always be transferred to the next bike (within the same generation, and some things with both earlier and later models). Do you drop your off-pavement bike?
Just look it over well, ask to see any records of services, parts, etc. Ask if it had sat idle for longer periods of time, etc.
"What is to give light, must endure burning."