My garage has said that my camshaft is badly damaged as the engine is making a tapping and grinding noise. There is no loss of power but the car is 12 years old. I have been told the engine won't take a new camshaft as it is to old, is that true?
They are most likely trying to sell you a new engine, you can find decent camshafts in junkers or on eBay.
They need to check if the camshaft damaged the engine head, if damaged occurred, then get a replacement engine head which should include a new camshaft, timing gear(s), and possibly timing belt.
Cost could range from $150 to $500, depending on the type of car you have.
I call bs on that, does your car have a reusable valve cover gasket? If so, remove the valve cover gasket so we can look at the cams or cam, take a pic of it. If it is flat like a circle without a pointed lobe, then your camshafts are shot.
If they're shot, then you can buy new ones OR pull them at the junkyard.
What car is it btw?
Tapping and grinding usually indicate failed lifters.
Here is a great video on how to check your lifters. If you push on them and they move down OR if they're collapsed before the cam lobe comes in contact with the lifter, they're bad and need to be replaced.
IF they cannot be replaced they CAN be rebuilt. Which is just cleaning them out.