Hi, code means car is running lean prpbably a emissions problem this could be caused by o2 sensor starting to malfuction or air flow meter. It could be the start of a minor problem but until it get worse you may not be able to pinpoint problem. I agree with mechanic probably nothing wrong and what ever is going on will eventually become more apparent . If you have any other questions let me know.
Not really the car could doing this for along time and you wouldnt do any damage the check engine light will come on permentantly before anything serios goes wrong that is its purpose.
If car is running rough or you start to see gas mile degrease even though you have a lean code that code easily turn to a rich condition if it is the air flow meter then it would be time to bring it to a mechanic
There probably more codes which help with diagnosis of problem. Code readers are pretty inexpensive now so if it is going to give you peice of mind it is worth it. Keep in mind places like autozone and pepboys will do it for free.