How old is the FTP protocol? Its history started 44 years ago and the first specification of its current incarnation was published 35 years ago. However, this October marks the 30th anniversary of RFC 959, which remained the authoritative specification of the FTP protocol ever since. Over the years, it has been updated and extended (most notably by RFC 3659 and the addition of TLS/SSL by RFC 4217), but never obsoleted. Even modern FTP clients and libraries such as Rebex FTP/SSL still work fine with 30-year-old FTP servers if you stay away from advanced functionality.
In terms of Internet history, 30 years is a very long time. It's therefore quite amusing that RFC 959 itself stated in 1985 that:
"FTP has had a long evolution over the years."
Obviously, the Internet was very young back then. The evolution of FTP started in 1971 with RFC 114. The beginnings were a bit rough (as described in RFC 686), but after several years, the efforts culminated in RFC 765 (published in June 1980). This was the first version of FTP in its current form and the first version to run over TCP (earlier versions used NCP instead). It lacked ability to create and remove directories or determine the current directory, but otherwise it was almost complete.
Even though FTP has its shortcomings (such as the notorious firewall-unfriendliness), it definitely proved useful and is still widely used today.