Re: 6 months = too old?
Lalaith, 6 months is absolutely not too old. In fact, lots of people from indigenous tribes in Africa and all over the world actually wait to start EC until the baby is crawling, so you're not too late. I would be really careful about doing naked diaper free time all the time. There is something to be said for using a backup and using it so that you're not stressed out and so that the baby has a reason to signal, so that's something to keep in mind.
With regards to your 3-month old, monkeyscience, it's absolutely not late either. You can really start EC at any age. I don't think it would be confusing if you put a cloth diaper over the potty but I also think that that might not even be necessary. Really, you can just decide what way you want to do it, what works for your family and for your situation, and at 3 months, your baby will definitely follow suit, so long as you do it with gentleness and confidence. Excited for you both!!!