is_older_than: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/lib/rc/bin/is_older_than - from package: openrc

You may install the required package with command apt-get install {package}

Error in other languages:
is_older_than: bevel nie gevind nie
is_older_than: comandă negăsită
is_older_than: comando não encontrado
is_older_than: commande introuvable
is_older_than: command not found
is_older_than: käsku ei ole
is_older_than: không tìm thấy lệnh
is_older_than: komanda nerasta
is_older_than: Kommando nicht gefunden.
is_older_than: kommandot finns inte
is_older_than: komut yok
is_older_than: nie znaleziono polecenia
is_older_than: níor aimsíodh an t-ordú
is_older_than: no se encontró la orden
is_older_than: no s'ha trobat l'ordre
is_older_than: opdracht niet gevonden
is_older_than: parancs nem található
is_older_than: perintah tidak ditemukan
is_older_than: príkaz nenájdený
is_older_than: příkaz nenalezen
is_older_than: команда не найдена
is_older_than: командата не е открита
is_older_than: 命令找不到
is_older_than: コマンドが見つかりません