Generally, there's a transition in growth when the plant starts to switch from vegetative to reproductive growth. The sidearm formation (where the hops are produced) seems to vary from variety to variety. Some begin to throw out sidearms very early and others much later. I think it all has to do with when the cones actually start forming. I've never really bothered to try to keep track of the whole process but have just let them do their thing. But, I have noticed that during the first year or two of growth, some do seem to push the laterals out a little early. Maybe like teenagers, their hormones get kinda whacked out and they try to be like the adults? I wouldn't worry about it as there's a lot of growing season left.