Q's about switching to Convertible seat

PhoebeJones3

Does it matter which age you make the switch? Most seats I've seen will take a baby as small as 5lbs. So I'm assuming its still safe for my 3 month 16lb baby. I'm not looking to switch right away since my Chicco will carry Parker up until 22lbs, but I'm planning on switching when its no longer comfortable to carry Parker around in his infant carseat (which isn't much longer since he is HEAVY)

I've searched and searched, and currently considering the Diono Radian RXT since I'll never need another seat after it and it goes up to 120lbs! Yes its costly, but I see it as paying for my child's safety and to me, that is priceless!

Any tips, comments, and words of wisdom would be greatly appreciated. Thanks!