If you have already viewed the car this reply might be a little late, but better late than never.
I own an '05 LS430, so can't comment on the age of the car, but with that mileage the car is barely run in. I have done similar mileage and have had no problems worth mentioning, which is what you'd expect given the quality and reputation of the car.
I can achieve 30mpg on a motorway run, but only with a light right foot. You should expect to get 27-28mpg without too much trouble. Around town it's a little different but you should get 22-23mpg. Unless, of course, your town is central London, in which case expect 16mpg.
Sounds like a good buy too me, but would repeat all the comments made by Peter regarding fsh etc.
Go for it, you won't be disappointed!
Bob