I started working with Unix as a hobby (to be anti M$) I got my first Unix Admin job in 1996, I had basic skills, I could build a box, do basic changes, create users, etc. I still have very little formal training, the training that I do have is Mainly Veritas Volume Manager, and Veritas Cluster training. I learned most by listening to Sr admins and a lot of reading (mostly man pages). Remember... Google is your friend ;-)
To answer your question No. You dont need formal education, but I am sure that it doesnt hurt. How you learn also plays into it... Most of the Unix people I know personally do not learn well from books, they learn best by jumping in head first and just doing it.