I am quoting from an article from the Ohio Conservation stationary on http://www.smallmouth.org/OhioC&R.html. The article is titled "Why Is It Important to Practice Catch & Release?"

It states stream smallmouth bass require 5 years to reach 12 inches in length. A 15 inch bass is seven years of age. This surprised me to be honest. When I was stream fishing back in the 70's and 80's, I use to catch a few in the 3 and 4 pound range in pools left by low water levels in the fall. I just didn't realize how many years it took for a smallmouth to reach that size and weight. I think I can appreciate smallmouth stream fishing a little more now.

This article urges us to protect our smallmouth streams by "Catch and Release" and follow state regulations and guildelines in order to keep our fisheries productive.