Often, there is no waiting period in a group plan, like one offered by an employer. Of course, if you were eligible for a company-based plan, you probably wouldn't be shopping around on your own. However, the same privilege might be had in a group plan offered through an organization such as AARP. With their plans, there's no waiting period for preventative services, at least.
No individual applying for health coverage through the individual Marketplace will be discouraged from applying for benefits, turned down for coverage, or charged more premium because of health status, medical condition, mental illness claims experience, medical history, genetic information or health disability. In addition, no individual will be denied coverage based on race, color, religion, national origin, sex, sexual orientation, marital status, personal appearance, political affiliation or source of income.