Not to be a negative nancy, but in all likelihood there’s serious vulnerabilities in the AOL client. If you connect to this, anyone else connected to it can probably pwn you. So maybe run it in a VM or something.
If that's the programming style that was deemed acceptable for release, I can almost guarantee you that the old, unmaintained client will definitely have some other vulnerabilities left over in its protocol.
[1]: https://www.geoffchappell.com/notes/security/aim/index.htm
Initially AOL's was done (GUI and non-GUI functionality) via their client API called FDO and sent assembled packets out like everything else. AIM on the other hand was a classic simple GUI app using a different protocol and used none of AOL's FDO stuff.
Much later AOL used some OSCAR (AIM) libraries to piggy back the AOL client on-to AIM for buddies and IMs, but even so these were not a part of the exploits that kept popping up for AIM, and long after AIM's drop in popularity as well.