Are you using the shortcut for sending to Terminal not console ? CTRL + ALT + ENTER is for sending to terminal.
Know that if you are using the AltGr + Enter, it is equivalent to Ctrl + Alt + Enter.
by the way, The command machine.age <- 4 means nothing to windows terminal hence the error. But I think you know that 
Sending to the R console is CTRL + ENTER most often or Alt + Enter but not AltGr.
Hope it helps