Why would you not renew it? Plenty of time until September. I don't know if US passport renewals are the same as UK, but with a UK passport they'll start the new period from the date of expiry of your previous one, so you don't lose any time renewing early.
US renews on the date that you renew it, not on the original expiration date. I lost a few months last year because I had to renew early to make sure I didn't have the "6 month" issue.
don't worry about the 6 month is an Airline policy following US CBP regulations but they make exception, if your passport is valid until six month later of your trip your good , if not they will check your return ticket. if is inside the 6 months your good. Remember in Mexico you can cross the border by car with your drive license. In other countries they strong enforce that policy you actually get deported. but in Canada and Mexico no worries !!!
