Hey Cycling@42 -
You've already got some great tips from this terrific TE group and I'll add my encouragement to the rest. Of course you can do a century in September! Just build on whatever you've been doing by following a training program, but be sure to adapt it for what you need - NOT for anyone else's. So, take what we're all saying,knowing that we're speaking from our own experiences, and find out how it all works for you. There is great advice here about eating, hydrating, training, etc, but you and you alone have to experiement with what works well for you. Do you need a certain kind of electrolyte drink? Do you gag on some energy bars or favor a particular gel or road snack? How about stretching, hydration, body mechanics on the bike (use your lbs to check you out while on your bike - saddle? bars?)?
Also, the 10% rule is a good guide - not adding more than that to what you've been doing each week, so that you build your endurance for long rides. Use speed/hill intervals about once a week to help make you stronger and faster but it's time in the saddle that counts most of all, so the suggestion to ride, ride, ride pretty much sums it up.
When it comes time for your century ride, you can just consider it 4 lil ol' 25 mile rides all rolled into one and it'll be a breeze! Happy trails!