It is something of an oversimplification to suggest that BMWs are designed to last ten years. Manufacturers design and engineer cars to last a long time, but not indefinitely, which is why manufacturer warranties typically do not exceed five to seven years or 100,000 miles. Also components that are considered 'lifetime' or 'non-serviceable' may start to show signs of deterioration after this period. However, with good maintenance almost any car can exceed 150,000 miles or more.

If you are suffering reliability issues with your BMW it may be that it is not the best example, so we would suggest making your decision on whether to keep it or sell it based on how well it serves your needs and if maintaining it is costing too much money, rather than basing it on the fact it is ten years old.