My 9 year old is doing algebra right now. The thing I've found is it's a very good thing to be able to write out diagrams and steps to longer problems. And just to have the patience to weed through them. The last few Singapore books really pushed this point. Which made me very glad we used Singapore! Singapore is nice in that it encourages deep problem solving skills, especially if you use their extra materials. So it helped slow us down a bit.
My own kid has understood many algebra concepts for a long time. But now his writing skills and maturity have caught up in such a way that I feel comfortable diving into a "real" written algebra curriculum. Every kid is different, so I guess I'm not comfortable with the 10 and up statement. YMMV. Had we done something like an online curriculum I'm sure we would have gotten here sooner.
