I don't think mileage is a good indicator of these bikes conditions.

The engines are known to be bullet-proof, there are many with close to and if not 100k or more on them with little internal wear.

I think the best factor is a well-maintaned engine.. regular oil changing and valve adjustment.

One of my NC24 riding friends over here has 76,000km on his bike and it starts and runs like new, but he's owned it since it was new and it is maintained properly..

Mine's over 50k and running sweet. Who's the other?

Service regularly and any problems I usually fix immediately. Have ridden continuously for the last 6 months. Probably done less than 500 miles in my car in that time. It's coming up to valve clearance time to just wanting to do that asap along with the usual balancing, plug/ air filter change etc then ready for a few trips and some more miles!

Ye olde NC24 has done a nudge under 47000km so about 29000mls , whether the speedo is correct
who knows for a 20 plus year old bike, although at some point its been someones pride and joy as they have taken either time or spent dosh and had the frame and swinging arm polished, why, gawd knows (a total ball ache) as its not been street fightered, but it starts, runs well revs right through the range, carbs need to be balanced, but thats a dark nights job, for £350 and err rising its the best fun toy I have ever brought

Just bought mine.had 50,000ish in kms so roughly 30,000. I think ill get the valve clearances checked for peace of mind.