A bit OT, but yes and no. The jailbreakability depends on the iOS version the phone happens to be on when you get your hands on the device. If it's too recent (say iOS 11, ATM), then good luck with that.

(Apple being Apple, you are normally not allowed to downgrade (yes, on certain terms it's possible, but you would need to have SHSH blobs saved earlier and I'm not sure whether even with those a downgrade is guaranteed). Nowadays, jailbreaking as a process is almost a joke compared to what it once was: recently the Windows jailbreak software is available first, Macs come second if at all, the jb might be a hit'n miss and/or riddled with bugs and usually you can't even upgrade to the latest jailbreakable iOS version at the time the jb finally is available as they come so late that a newer iOS version already exists. So you would often need to lose a previous jb by upgrading beforehand at the moment there's even a hint of a jb for whatever iOS version Apple allows you to upgrade and hope for the best all the while using your phone without a jb.)