Do you have a citation for this? I've had some stretches in my career where I went a long time without doing any significant coding, and have always been able to ramp back up to speed quickly when needed.
Even in my own life, I was a developer from 10 to 18 (working 14 to 18, school 10-14) then I took about 7 years off to go do physical sciences. While I retained the basics like for loops and function calls, I totally lost a good portion of the rest of it.