mid-14c. (mid-13c. in surnames), "commercial agent, factor," also "an agent in sordid business," from Anglo-French brocour "small trader," from abrokur "retailer of wine, tapster;" perhaps from Portuguese alborcar "barter," but more likely from Old French brocheor, from brochier "to broach, tap, pierce (a keg)," from broche (Old North French broke, broque) "pointed tool" (see broach (n.)), with an original sense of "wine dealer," hence "retailer, middleman, agent." In Middle English, used contemptuously of peddlers and pimps, "one who buys and sells public office" (late 14c. in Anglo-French), "intermediary in love or marriage" (late 14c.).
word-forming element in nouns of act, process, function, condition, from Old French and French -age, from Late Latin -aticum "belonging to, related to," originally neuter adjectival suffix, from PIE *-at- (source of Latin -atus, past participle suffix of verbs of the first conjugation) + *-(i)ko-, secondary suffix forming adjectives (see -ic).
Others are reading
<a href="https://www.etymonline.com/word/brokerage">Etymology of brokerage by etymonline</a>
Harper, D. (n.d.). Etymology of brokerage. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/brokerage