Mo. Rev. Stat. § 516.030
If any person entitled to commence any action in sections 516.010 and 516.090 specified or to make any entry be, at the time such right or title shall first descend or accrue, either within the age of eighteen years, or mentally incapacitated, the time during which such disability shall continue shall not be deemed any portion of the time in sections 516.010 to 516.090 limited for the commencement of such action or the making of such entry; but such person may bring such action or make such entry after the time so limited, and within three years after such disability is removed; provided, that no such action shall be commenced, had or maintained or entry made by any person laboring under the disabilities specified in this section, after twenty-one years after the cause of such action or right of entry shall have accrued.
§ 516.030, RSMo