The age can vary, especially depending on how old the scion stock used for grafting. If the stock plant was flowering, the newly grafted plant can also. The maturity is passed from the graft scion to the new tree. All the growth thru the scion will have some of the same mature charesteristics. I think stress, like draught, etc can also cause the tree to try and propagate itself.

I have several 1-2 year with flowers. Its funny to see them on such small plants. Maybe 10 leaves, and almost that many flowers.

I think seedling grown trees flower at maybe 7 years or so. Not quite sure of that number, others may know exactly.

The cultivars like yours, especially dissectums, dont show as much tendency to flower. So if they become viable, that would be great for you.

Mike, Acer palmatum 'Crazy'