In Romanian, you wouldn't refer to someone as being "larg / largă" (unless you have a dirty mind :). That's why there's no pronoun here. The resemblance to the English "large" is unfortunate, since "larg" generally means broad, wide, vast, or (when referring to clothes) loose.
Because in Romanian, you wouldn't refer to some person as being "larg / largă", so "he" or "she" don't go well here. Hence, the only possibility left is "it", which is a thing, not a person.
"El nu e mare", but you would generally either insert more context or rephrase it to clarify the meaning. By saying "He is not large", you could mean that he is not fat, muscular, tall, or any combination of these. The same applies to "El nu e mare" in Romanian, with the addition that it can also refer to someone's age, typically when talking about children or youngsters.