“Person under legal disability” means a person 18 years or older who (a) because of mental deterioration or physical incapacity is not fully able to manage his or her person or estate, or (b) is a person with mental illness or is a person with developmental disabilities and who because of his or her mental illness or developmental disability is not fully able to manage his or her person or estate, or (c) because of gambling, idleness, debauchery or excessive use of intoxicants or drugs, so spends or wastes his or her estate as to expose himself or herself or his or her family to want or suffering.