A 21 year old who makes $30,000 a year will be able to opt out because he or she will be paying $2,637 premium without receiving subsidies, which is 8.2% of his or her income. The math actually works for people who earn between $27,000-$33,000.
A 64 year old who person who makes between $27,000 and $99,000 a year will be able to opt out.
A family of four at age 21 can opt out between $55,000 and $88,000.
A family of four at age 64 can opt out between $55,000 and $268,000.
Note: This is assuming the reconciliation proposal is adopted and using the calculator found here:
http://healthreform.kff.org/SubsidyCalculator.aspx