Some groups of people are categorically eligible for Medicaid. That means they are in a category that may make them able to get Medicaid. These groups include families with children and people with disabilities. This only means that you may be able to get Medicaid -- not that you automatically get it.
As part of the Affordable Care Act, you no longer have to have young kids to be able to get Medicaid. But you cannot make more than a set amount of money a year to qualify for Medicaid. How much you can make depends on the state where you live.