A spike buck is older than a yearling, but not 2 years old yet. He was a late fawn of the spring before, so the spike is his first rack.
What I mean is this. MOST does are bred in November, their fawns born say in June. Well, a spiker's mom was bred say in late December early January, so he wasn't born till say late July early August. He wasn't able to grow a "rack" the year he was born, so the spike is, for all intent and purposes here, the same as a button buck. We all know that a button can grow a big rack, and so can a spiker.