My child is 18 now. Can I claim he/she as a dependent?
Generally, as a parent or a guardian or a foster parent you may claim any dependent who is not over 18 or who is not yet 24 and is a full time student. The primary issue is the question of the amount of income earned by the child in the tax year.
Further, regardless of the age, a parent may claim a child who lives with them if that child had no income, or if that child is disabled.