My first folk festival was Saddleworth 2009, and since I didn't actually go to any ticketed events or stay overnight I'm not sure even that counts. (I wasn't really into folk music between about 1975 and 2005, which may account for it. Also I don't like camping.)

The OP reminds me that the first (only) time I saw Steeleye live was also the first (only) time I saw Richard Digance, who was supporting them; he was hilarious, more or less from the moment he walked on (Hello, good evening and welcome to Folk Club, my name's Roy Harper...). Top gig, although not at a festival.