That sounds like a reasonable estimation. This bridge appears to be constructed with riveted connections. Rivets began to fall out of favor in the years after WWII as bolted and welded connections became popular.
20's to early 40's it's looking like?
This is a rare example of a Pratt - Warren Hybrid. There was another example in Johnson County Kansas, but it has been replaced.
Neat one - just on northern border of sleepy little RR town
A view of the bridge on Bing maps: http://binged.it/RPmvST