I left DS1 rear facing till 14 or 15 months, I only turned him as he was getting a new car seat at 18 months when DS2 was born.

I had many people comment on me being mean etc for not having him forward facing but I have watched the youtube clip on test dummies and wanted him rear facing as long as possible, DS2 will need to be turned earlier than DS1 due to weight as he is a bigger baby than DS1 was.

Our seat is also 12 kg rear facing and my guess would be DS2 allreaday 10kg.