can't be too careful with those lungs, especially if you're still a pup
I used to work with a guy who developed asthma from breathing sawdust everyday- he had a tough time with it- he was pretty young, had only been working as a carpenter for maybe five or six years.
like I said, some types of sawdust seem to be worse than others, but probably the best bet is to always be careful when you're sanding or doing something that creates really fine sawdust.