Car seat help

So My child is in a five point harness he’s 3 1/2 and around 60 pounds the weight limit listed says 65 for 5 point harness does that mean I have to get a different car seat to support more weight. He’s definitely not ready to go without as his sister is almost 6 and we still use the 5 point harness on her. We have the grace transitions 3 in 1 harness booster seat