There is no age limit on the 529 plan, but the utility of the plan diminishes significantly with time because there is less time for the money to grow.
If your child will be attending school in the next year or so, there is little benefit to the plan, as there will not be much growth/tax savings.
You will get a small benefit from the state income tax deduction (if your state has one), but this is often very minimal. We only save about $100.00/year in state income tax using the 529.