Yeah, you can get faster if you don't have a lot of races/times. You can train better, and race smarter. Work on the bike and the transitions.
I'm not fast..best marathon at 40 - 4:44:02, lots of 2:20 halfs, mostly 1:10 - 10 k's and 35 min 5k's these days. I started with 1:50 sprint tris and was consistent with that time for 6 years until 2012. I added weight training to the swim-run-bike cycle, and did more events (3 in 2012 and 4 in 2013) and went under 1:45 consistently including 2 x 1:40. Gains all around, but mostly a faster bike time, and something left in the legs for the run (thank you evil personal trainer Kevin and your leg workouts!)
My next goal is to go under 1:40. I don't think this will be the year, since 'the move' and all it involves has really impacted my ability to get to the gym. Oh well. Next year I go up an age group (55-60)!
FWIW, it is the 'career' athletes who experience the decline after 40 the hardest. Having competed at such a high caliber from youth, the effects of age are truthfully reflected in older age. Older 'fitness lifestyle' amateur athletes who compete less frequently might change things up a lot between events-loose weight, train better, invest in better equipment, learn efficiencies, eat better, etc. and this can translate to better personal times.