Cody got a commercial version of the Chromebit for Christmas and he can't install Android apps to it. Leo says not every ChromeOS device can do it and it's likely that the Chromebit he has can't do it because it doesn't have touch. It may also be that he hasn't gotten the update yet and once he does, he'll have access to the Play Store.
Leo also explains that it's possible to code with ChromeOS. There are several websites that would allow Cody to code within the Chrome browser. Cody can check out Bootstrapworld.org. He should also check out WeScheme.org.
Cody also wants to know if he can root his dad's old Android phone and put a new version of Android on it. Leo says yes! He should go to XDA-Developers.com and look up the exact model of the phone and he'll get directions on how to do it. If there is one, he'll be able to. He may need to use a Windows machine with the Android SDK to do it, though. But it's definitely doable.