That depends on how you define "protocol". ASCII dates from 1963, and that's still the baseline for text-based protocols.
FTP predates Ethernet, Token Ring and ARCNET. It predates TCP/IP. For an actual protocol, and not just a simple format specification like ASCII, it doesn't get older than that in current use.
ASCII is a very obvious format. If you take the english alphabet and symbols, it fits almost perfectly in the first 7 bits. In 5th grade I tried encoding English in binary, and noticed how I accidentally reinvented ASCII.
I wouldn't say it's obvious. There's some careful decisions in the design that might not be obvious at first sight, such as having upper and lowercase characters be the same save for a single bit.
FTP predates Ethernet, Token Ring and ARCNET. It predates TCP/IP. For an actual protocol, and not just a simple format specification like ASCII, it doesn't get older than that in current use.