It depends on the type of IRA you are. Almost anyone can contribute to a traditional IRA, as long as you (or your spouse) receive taxable income and are younger than 70 and a half years old. However, your contributions are tax-deductible only if you meet certain requirements. For more information on those requirements, see Who can contribute to a traditional IRA? Yes, you can contribute to an IRA for a non-working unemployed spouse with whom you file a joint return, but your total combined contribution cannot exceed your joint taxable income or double the annual IRA limit, whichever is lower.
The five-year rule of the Roth IRA states that you cannot withdraw earnings tax-free until at least five years after you first contributed to a Roth IRA. Converting a taxable retirement account, such as a 401 (k) or a traditional IRA, to a Roth IRA, has no impact on the contribution limit; however, making a conversion increases the MAGI and can trigger or increase the gradual reduction in the amount of your contribution to the Roth IRA. If you make too much money, you may still be able to contribute to a Roth IRA using a strategy called a clandestine Roth IRA. Every year you make a contribution to a Roth IRA, the custodian or trustee will send you Form 5498, IRA Contribution Information.
Yes, a person under the age of 18 can contribute to a traditional Roth IRA or IRA as long as they meet earned income requirements and don't earn more than the income limits.