The state of being old. 2. Sometimes in this state it is exceedingly difficult to know whether the individual is or is not so deprived of the powers of his mind as to be unable to manage his affairs. In general, senility of energy in some of the intellectual operations, while the affections remain natural and unperverted; such a state may, however, be followed by actual dementia or idiocy. 3. When on account of senility the party is unable to manage his affairs, a committee will be appointed as in case of lunacy.
SENILIT
TheLaw.com Law Dictionary & Black's Law Dictionary 2nd Ed.