From Longman Dictionary of Contemporary Englishfull-grownˌfull-ˈgrown American English, fully-grown British English adjective ADULTa full-grown animal, plant, or person has developed to their full size and will not grow any bigger A full-grown elephant may weigh 2,000 pounds.
Examples from the Corpus
full-grown• We could see them clearly then, a male and a female, full-grown adults.• A full-grown antelope was lying by the trail.• Full-grown female whales are about one-third the size of an average male.• And the name is quite accurate -- these cars are actually one-fourth the size of their full-grown kin.• One was a tall, handsome, oversized athletic fellow, who at thirteen already looked like a full-grown man. 