If it's in good/excellent mechanical and cosmetic shape that is a steal IMO.
Even if it looks good, ask him the history of the bike, how many owners, how was it treated & rode, maintanence history and stuff like that. If he is the only owner and hesitates on any of his answers, something may be wrong and you should proceed with caution.
How it was rode is especially important. 5500 on-road miles is nothing and it should easily go many many more, but if it was 5500 miles of nothing but WOT steep hill climbs in 1st/2nd gear in 100+ degree heat the thing is probably about worn out and ready for a rebuild.
The most miles I've heard of on a TW with no rebuild is 47,000 and rising, by qwerty of this forum. That shows how far even a small air cooled bike can go with excellent care, and he will probably get many more miles before it's ready for a build.