The first time I rode to work (13 miles one way) I was horribly out of shape.. the effort nearly killed me and it took nearly an hour longer to get there than it does now. Before that i'd only ridden about 2 miles at one time, but the feeling of accomplishment and freedom it gave me.. I was hooked after that..

6 miles one way shouldn't be so bad if you take it slow and gear low till you feel like you're ready for more effort, assuming there aren't many hills.