first major thing u need to know is that:
a BMW that is a car is a BIMMER
a BMW that is a motorcycle is a beemer/beamer.
haha lol, well, ^ that is true though
many people here on these forums have bmws that have over 200 thousand on them, if u are 150k, dont worry about it, as long as the engine sounds nice and there is no oil leaking, or burning, or on the valve cover gasket..(which u will notice if there is.. if the engine is dirty from the top.. or even the bottom) .. anyway if none of those things apply, dont worry