If we're going by tradition (i.e, what has been common throughout history) were typically between two closely aged people (historical average age of marriage for women is early 20's (21-23) while for men it's early-mid 20's (23-26). So if we're talking about an arranged marriage between, say, a 16 year old girl and an 18 year old boy, yeah, that's fairly normal. In fact, most states have romeo and juliet laws or parental consent laws as explicit carveouts for this kind of thing.
The objection comes in with something like picrel- "young brides" and "military aged men" are vague and relativistic terms, that, if read in the context of other stuff being posted, would suggest pairing off 15 year olds to 27-35 year olds. This is not traditional, particularly within European (White) culture and reeks of furtive dual-motivations.
