If you open an additional American Express card account, such as the Starwood Preferred Guest credit card, it will have the same Member Since date as the JetBlue card -and- it will be reported to credit bureaus as if it had been opened in the same year. You can safely close the JetBlue card account, and you will probably be able to transfer some of the credit line to the SPG card. Alternately, you can ask about converting the JetBlue account to a free card such as the Everyday card, or one of the Blue cards.