Hi Bradley
thinking of trading up then? 100k miles is nothing to a car nowadays but the values drop like a stone when they hit that mark so bargains galore!
The A5 is a great car and as far as mileage goes, it affects residual value but otherwise, the engine should still be healthy (if maintained) for thousands of miles more.
As for the rest of the car, you'll need to have a thorough check of all components for wear and tear but full-service history should eliminate any major problems.
Keep us updated on what you find out there.
Cheers, Trevor