When should I stop using Nuna PIPA?

I'm curious, under what circumstances would you recommend stopping the use of the Nuna PIPA? Are there any specific safety concerns or age milestones that parents should be aware of when it comes to transitioning their child to a different type of car seat? I'd appreciate any guidance on when it might be time to retire the Nuna PIPA and move on to a different option for our growing child.