Papers almost always have some indication of a deceased person's date of death and age. Recorded at a county courthouse. Found at state level. May mention schools attended, vitals and more. Available at National Archives.
Applications are full of genealogical evidence.
Private company records, but if person is deceased, they may be open to inquiries. Filed at the state level health department and may include vital information about the deceased, including date and place of birth. Date of application is a clue to the person's age, but some will give age and residence of the petitioner. Filed at state land office, state land states. Usually identifies a person with basic vitals, but submitter of the query needs to be contacted.