Viking is a profession, not the faction. AoE2 unfortunately perpetuated historically inaccurate depictions of the Norse including horned helmets.
Kalmar Union would be the proper term for the nordic factions as a full scale high medieval empire. You could also choose Danes, Norway, or Swedes if the Kalmar Union is too late into the time period.
Calling the faction “The Vikings” is like calling the English as “The Pirates”, or the French as “The Farmers” or the Chinese as “The bureaucrats”
