I don't know for sure, but I would imagine lernanto is just one who is learning in general, while lernejano is a student at a particular scool.
Jes, vi estas lernanto de Esperanto, ne lernejano de Esperanto (aŭ eble via lernejo instruas Esperanton, mi ne scias) :D
In addition to "pupil"which denotes someone not in college or under 18 one uses the word "learner" ?
*student/o. Persono, studanta en universitato aŭ alia simila supera lernejo
So that one is clear-cut. But you may be right that lernejano might be used to refer to college/university students, since a college or university is also an "ejo por lerni". However, it's worth noting that the Vortaro.net entry on lernejo refers to instituto, gimnazio, kolegio, liceo, seminario, vartejo, but not universitato.
((You might say "well, kolegio is in there", but in its own entry kolegio is marked as a "to be avoided" word, because it is both used to refer to the English meaning of "college", and the French meaning of "collège" (junior high school), making it very ambiguous.))
I chose apprentice but it wasn't approved. Is it the wrong word? Can anyone tell me why it's wrong?
An apprentice is someone learning a trade, usually by watching a more senior worker. They're not in school.