The word for male human was “wer”, for female human was “wīf”, and while “wīfmann” and “wīfcild” are attested, “*wermann” and “*wercild” remain hypothetical and are unattested.
Perhaps the word existed, and it would no doubt be understandable to any speaker of Old English, but it did not show up in any text, nor did any of it's descendants survive into modern English.
There is a general trend in languages for female terms to display markedness, consider that there is no term for a specifically male actor in modern English either, though in some contexts male terms display it, such as the coinage of the word “murse” to refer to a specifically male nurse.
Neutrality of words in actual use is not so simple, in any case, though it is true that the word could clearly be used to describe human beings regardless of sex, as it still sees use today:
> God ġesċōp æt fruman twēġen menn, wer and wīf.
> God created at the beginning, two men, a male, and a female.
Usage of “mann” in O.E. to identify a single, singular female man was quite rare, as it still is today, outside of compounds such as “crewman”, but some attestations do exist, similar to the Latin “homō”, for which it was similarly rare and other words were typically used.
One may be left to conclude that, though it was theoretically possible, it was stylistically not common, similar to how, perhaps, the word “actor” was used a century back where “actress” was quite often used for a female actor, al the while acknowledging that “an actor”, hypothetically speaking, could be any sex, and “actors” could easily be used for a mixed-sex group.