Late Roman Army - seniores and iuniores

[Ti Cl Nero]

Salve Jens,
this suggests newly recruited units would not be designated "iuniores" - you mean this, don't you?
I agree, this also makes sense to me.
While the term "iunior" is widely used (as "tiro " does) in late empire sources (Vegetius, De Rebus Bellicis, Codex Theodos.) in order to designate recruits, I would think that designating a unit following this principle would be not logical: soldiers would not like to serve in a unit which would indicate themselves as "recruits" even when they were no more such ( I guess supposing "iuniores " units constantly kept as recruits-composed units is illogical as well)
If a link with the "age matter" has to be found, I think it should be much less direct.
It may be related to the chronological hierarchy between the 2 units bearing the same name; in this, Nicasie may be right at least under a general point of view, if not in details: maybe a iuniores unit was created out of an existing unit (which would then became "seniores"); the "seniores" would supply a skeleton of officers and veterans to the new unit, whose gaps would have to be filled with new recruits.
In this case, the new unit would still be mainly composed of recruits when formed up, but the designation "iuniores" would be seen in a more general meaning , with a reference to a "seniores" parent unit rather than to actual soldiers' status.
Just a possibility, anyway, without conclusive proofs - I found this principle plausible, while details may be widely varying.
If, on the contrary , I didn't catch your point, Jens, I apologize.