In many cases, the version of Go (golang) provided by the system is old. Getting the latest Go by downloading a tarball is expedient but hard to manage.
Here are some ways to get a latest (or nearly latest) Go through a package manager.
This is prompted in part by Minimum Go version requirement #79, a requirement in the Packet CLI that the build environment support at minimum Go 1.14 because of dependencies.
Ubuntu
From the Go wiki
If you're using Ubuntu 18.04 LTS or 20.04 LTS on amd64, arm64, armhf or i386, then you can use the longsleep/golang-backports PPA and update to Go 1.15.
sudo add-apt-repository ppa:longsleep/golang-backports
sudo apt update
sudo apt install golang-go
Debian:
If you're running Buster (Debian 10), buster-backports has golang 1.14. Linuxhint has instructions on how to use backports on Debian, if you are not as familiar.
FreeBSD
FreeBSD 12.1 gets Go 1.14.7 as of this writing; I didn't need to install any other tools in order to upgrade.
MacOS and Homebrew
brew install go; brew upgrade go
gives me Go 1.15.