How do you find out how old your Daisy BB gun is?

If it's a Daisy Red Ryder then they have been in production since 1939 up to today. Look at the model number on the barrel. It will say something like no-111 model 40 or 1938B. This is a starting point. Then see the link below. It's Daisy's web page about answering questions about your old daisy. fill out the information and they will help you.