Robin, the large seedling is 9 years this year, but it is in competition with mum, so may have got bigger if planted on its own. Have a self sown seedling in the back which is on its own and is the same size in 7 years.
Mo, the rounder leaved ones seem to have longer individual leaflets and are more prone to wind damge, The ones with a less full leaf the leaflets are fused for more of their length giving a tougher leaf. At the other end of the scale some are more delta shaped with leaflets fused for 3/4 of their length
Fletch, they stay samller in small pots, particularly if allowed to dry out. They are surprisingly drought hardy, but don't grow their best in dry conditions.