In the Original Rules as written :
This line of text from Vol. 1: Men & Magic of the LBBs says a lot to me about the nature of elves in the game and when it is adhered to, makes White Box a very unique fantasy roleplaying system. White Box assumes a human-centered milieu, one where most player characters and NPCs will be human. Elves exist, as do the other "good" races of dwarves and hobbits as possible player character choices, but each of these is limited in class choice and level of experience which can be attained, perhaps making them less appealing to play than humans. Dwarves and hobbits are limited to Fighting Men. Humans can be Magic Users, Fighting Men or Clerics and can advance to any level allowed in the campaign. Elves are limited in level, but have the unique quality of switching from Fighting Man to Magic User and back.Elves can begin as either Fighting-Men or Magic-Users and freely switchclass whenever they choose, from adventure to adventure, but not during thecourse of a single game.
In the implied milieu of the White Box as written, humans devote themselves to the study and mastery of either fighting or using magic. Fighting is about Strength and magic uses Intelligence, hence the Prime Requisite Abilities and experience bonus and penalty associated with high and low scores in each. Body verses mind. A dichotomy, if you will, one that places development of body in opposition to development of mind. Fighting Men learn no magic, unless they change class which requires a high score in the Prime Requisite ability of the caster class and they presumably progress no further in the old class. In effect abandoning all efforts at improving along the lines of the old way.
The Cleric, who uses Wisdom as their Prime Requisite, seems in some ways to be a combination class in that they are reasonably good at combat and have some spell casting ability once past 1st level. Only a human player character can choose to be a Cleric. If non-human clerics exist, they are not adventuring types. The Cleric class says a lot about the implied milieu of White Box and deserves its own discussion.
Elves begin play as either a Magic User or a Fighting Man - casting one 1st level spell per day and limited to a dagger and no armor in combat as a magic user, or as a fighting man they may make use of any available weapons and armor they can afford. To hit rolls are the same using the alternative system for combat, but their fighting capability using the Man-to-Man system in Chainmail differs with the Fighting Men gaining a +1 advantage. All weapons do 1d6 damage in White Box and there is no bonus for high Strength scores. Saving throws follow the most advantageous.
So what does this say about elves as a unique race of beings. (Assuming this isn't just a rules convention and nothing else.) All elves presumably act this way - at least the ones found adventuring. Elves are trained in fighting skills and have magical ability, either innate or acquired through training. The fact that the elven character must choose to act as either a Fighting Man or a Magic User for the duration of a single adventure implies there is some preparation and/or mental attitude necessary that precludes acting as both classes simultaneously. Wearing non-magical armor inhibits casting magic spells while acting as a Magic User. Borrowing from later editions, we might say spell casting requires a freedom of movement not easily done while wearing armor, or that armor, especially that of (non-magical) metal, inhibits the casting of Magic User spells. I imagine the elf preparing for a day of adventuring by either studying the spell book and memorizing a number of spells, or donning armor and strapping on weapons...not both, for the elf will act as either a magic user or a fighting man during this adventure, not both.
This "bipolar" nature (magic user - fighter) and the illustration of a bearded fellow wearing an outfit and long cap similar to a "Santa elf" casts the White Box elf character in a very different light than we see in later editions of the game. In some ways the White Box elf seems more consistent with the separation of magic use and arms and armor. If they are mutually exclusive for humans, why do elves get a "pass" in some later editions and get to both wear armor, and cast magic spells? That almost seems more inconsistent internally with a rational understanding of how magic works.
Elves are perhaps the most diverse demi-humans in terms of interpretation across editions and settings. Ear length, absence of facial hair, average height and build, even available character class all seem to vary among elves from one setting to another helping to make each milieu unique. The classic White Box elf, who can alternate between a Magic User or a Fighting Man, seems the most unique of all.