I live in the Alps which is about as hilly as it gets. My commute is 43 miles round trip with a little over 3000 ft of climbing. Like the OP, I'm 43 yrs old and ride a Trek FX (although mine is a 7.7, and it shares commuting duties with my surly crosscheck and cannondale touring bikes). I swapped the rear cassette on the FX to an 11-34 and the RD to a Deore XT, which made a big difference on the days when I'm tired. The hill climbing gets easier, but it takes time. Keep at it.