Any detailed examination of the tarot court cards will inevitably encounter the confusion surrounding the different titles given to the cards over their 600-year history. In early decks like the Tarot de Marseille, it was transparent: the cards showed the members of a medieval royal hierarchy. The Kings were seated on thrones, variously bearded and suitably august in appearance; the Queens were also enthroned and were clearly the mature female counterpart to the Kings; the Knights were horse-mounted, appearing vigorous and war-like; and the youthful Pages (sometimes called Knaves or Valets) were standing, befitting their role as squires to the Knights. This arrangement endured for several centuries, and fortune-telling custom was to treat the court cards as people involved in the querent’s circumstances. Arthur Edward Waite and Pamela Colman Smith retained it in their eponymous deck, although the Kings, while still grave, were no longer bearded.
The advent of esoteric interpretation in the 19th Century dropped a very large rock into the placid waters, and the ripples are still felt to this day. Suddenly, it wouldn’t do for the most powerful, virile and commanding members of the male court to be shown by the dignified but sedentary Kings; they had to be warrior-kings mounted on steeds. At first they retained the title of “King” in occult systems but that would soon change because the image of the Knight already conveyed the necessary “alpha male” symbolism. However, it was unacceptable for the newly unseated Knights to fully assume the stationary posture of the Kings due to their inherently active nature, so they were given chariots as an emblem of their still mobile but now less assertive presence. It was all well and good to retain the title of King for the dominant, mounted male, but the Knights had to change in both appearance and nomenclature to reduce confusion; so they were renamed Princes, and the Pages were recast as Princesses to balance the gender equation. (We will set aside the fact that, for a while, the chariot-borne Knights in the Golden Dawn model were renamed Kings and the old Kings were given horses and became Knights.) What was originally a purely hierarchical structure became a more familial one: Father, Mother, Son, Daughter. Ultimately, Aleister Crowley reaffirmed the swap by changing “King” to “Knight” in the Thoth deck while retaining “Prince” and “Princess.” Some writers have taken pains to point out that the Thoth Knight and the Waite-Smith Knight are not equivalent; the former carries the full authority of the royal monarch (King) while the latter retains the subordinate role assumed by the Prince in the Thoth design .
A final word on age. Contrary to common sense, Waite positioned his Knights as “males over 45” and his Kings as being under 45. I can only assume he caught the Golden Dawn’s provisional “Knight-Queen-King-Page” iteration mid-stride and never retracted it (and I’m not aware that he ever offered a convincing justification). My opinion is that it’s most logical to define the Kings (Thoth Knights) as older males (45 is a reasonable “cutoff point” since it is more about mental and emotional maturity than physical prowess), the Queens as their female contemporaries, the Knights (Thoth Princes) as people (whether male or female is open to case-specific adjustment) in the physical prime of life (25-45) and the Pages (Thoth Princesses) as young people of either sex under 25. In all cases, the nominal gender is not a given and should be assigned by the reader to suit the context of the question or matter at hand.
A more detailed discussion of the “King/Knight” conundrum can be found here: