According to Merriam-Webster's Collegiate Dictionary, 10th Edition, the noun maturity dates back to the 15th century. I think the implicit, unstated definition of maturity goes well beyond all that. When people refer to another person as being in a state of maturity, they are assuming several things, not the least of which is the individual upon whom they are placing this noun has an open mind. When a person is able to see beyond the scope of his or her own beliefs in order to comprehend and appreciate someone else's viewpoint, then and only then can it be said a state of maturity has occurred. Ann Landers recently ran a column which I think captures the true spirit of maturity.
Maturity is the ability to control anger and settle differences without violence.
Maturity is patience. It is the willingness to pass up immediate pleasure in favor of a long-term gain. Maturity is perseverance, the ability to sweat out a project or a situation in spite of heavy opposition and discouraging setbacks. Maturity is the capacity to face unpleasantness, frustration, discomfort and defeat without complaint or collapse. Maturity is the ability to make a decision and stand by it.