Yes, Shifters are required to begin at their most basic evolutionary stage. There are actually two in-game characters, Tiki and Yukari Yakumo, who are also shifters who specified that they de-evolved due to having had a long slumber in their backstories so you may say that he WAS at one point an Aegislash but is no longer, should you wish to go that route.

In this case it wouldn't necessarily be an issue as you'd be starting as a level 8 Honedge but yes, Shifters can generally relearn basic moves at a rate of one per week that they could learn Egg and Tutor moves.