Like most referees, a soccer referee really has to be in good shape. They are doing a lot of running up and down the field without much break.
My brother belongs to a soccer referee association and has worked his way up to a college referee.
At this level, the pay is pretty good and the competition is stiff. This also involves a lot of travel, so he is on the road quite a bit.
A love for the sport is how he became interested in becoming a soccer referee. Both of his sons are also on soccer teams in their age brackets, so I wouldn't be surprised if it doesn't stay in the family for a long time.