Earned income remains taxable regardless of age. Similarly, such income continues to be subject to Social Security and Medicare taxes (FICA for an employee; self-employment tax for a self-employed person). The one age-related break: once a worker reaches the full retirement age (currently 66), then he/she can have any amount of earned income without a reduction or complete loss of Social Security benefits.
A retirement account to which up to $4,000 (or $5,000 if you are 50 or over) may be contributed for 2007, but deductions for the contribution are restricted if you are covered by a company retirement plan. Earnings accumulate tax free.