The Royal Elite Guard is a special group of soldiers from Alec's time period and kingdom, 700 years ago. The soldiers ranked higher than your average army footmen, as these were the ones who maintained the guard of the king and his closest family members. There are typically no more than about 20 members of the Royal Elite Guard at a time, and only the more accomplished young men are inducted into its ranks.
A term in the Royal Elite Guard lasts for ten years. One of the stipulations to for those who join is that they must refrain from all romantic relationships until their service is finished.
Alec was just barely inducted before setting off on his mission to defeat The Witch. His father had previously been part of the Royal Elite Guard, and was quite popular among the citizens of the kingdom because of it.