In the gang, an associate is a person who is not yet an OG, who is an "original gangster", who is high-ranking. Associates are from their teen years to the early twenties generally.
In the mob, an associate is a rank that is right below the rank of soldier, meaning that you are not yet a made man, which means that you are not a "full" member of the Mafia. Associates are generally non-Italian, as this is the last rank that non-Sicilians or Neapoitans can be. Famous mob associates include turncoat Jaggy Jovino, Angelo Granelli, Jimmy Conway, Tommy DeVito, Henry Hill, Marty Malone, and Georg Reisdorfiev. They are not as privileged as soldiers, but their tributes paid are less than an enforcer.
Associates can either be a higher level of enforcer, of a person "associated" with the mob, such as a shopkeeper or racket boss who run their business for the mob's profit. Reisdorfiev was a racket boss for the Barzini crime family, and was a Russian-American associate of theirs. Meanwhile, DeVito was an Italian, but was not a soldier yet, so he was an associate.
In gang terms, an associate is just a regular gangster. They are like the outsider in a Mafia family, just ordinary people. They are from ages 7 to 18, and they are usually runners, lookouts, or people sent out to do graffiti. They walk, talk, and dress like gangsters, and socialize with older gang members. They are like OGs, but are less committed to the gang lifestyle.