Wow, thanks for your service and that of your family! Thankfully, there’s no connection between the new Roth TSP and your grandson’s Roth IRA. He can actually do both without impacting the contribution limits of either. For those under age 50, $5,000 is the Roth IRA contribution limit while $17,000 is the limit for the TSP. Although, if your grandson or other servicemembers are serving in a tax-free combat zone, contributions made don’t count towards the $17,000. In that case, the maximum total contribution to the TSP would be $50,000. That would be some serious tax-free potential!