Another planned project that is yet unfunded is replacing signage from exit 32 to exit 52 vic on I 84. It was put up in 1985, by the time the project gets underway those signs will be 30 years old. The signs on I 84 East of manchester are CA 1995. In CT that's "new" signage. By our standards those will likely be there until about 2025.
I'm guessing signage on CT 25 is the oldest in the state... early 80s?
I-84, Exit 32 to 52 ... wouldn't say 1985. The I-84/I-91 interchange project wrapped up in the early 90s and the signs are pretty much from that era. Those around the 72 junction were replaced in the past few years. That takes us up to Exit 35. Those from there up to Hartford appear to be relatively the same vintage as those right at 91. Of course the ones at Exit 39A were put up in 1992.
I'd give second place would have to go to I-84 from Exit 57 to Exit 64. You can tell by the size of the route markers (though not the interstate ones anymore as most of them have been replaced). But look at Exit 64-65 EB / Exit 64-WB. This probably dates to the mid 1980s, when I-384 was connected to I-84, and the whole "frontage roads"-esque system went in.
Third place.... I-395 - mid 1980s, possibly tied with I-95 - Stratford. We'll most likely lose the I-95 section when the Moses Wheeler Bridge project wraps up. I did see I-395 signage mentioned in a long-range CDOT plan.
Fourth place.... to keep this post ON TOPIC, I'm saying I-91 from East Windsor, north to Enfield / MA state line. I'm giving them an installation date of late 1980s, as this was the first part of I-91 to be reconstructed, and I remember traveling north to VT in 1990 and seeing Phase III. Back in those days, Mass. still had an earlier generation of signage, where I recall much more pull-through signage, LEFT 2 LANES used instead of LEFT LANES, and a Northampton/Greenfield pullthrough on the Exit 13 gantry.