At 3+ months old a discus growing at a normal rate would be about 4 months old and you say you have had the several months which would put them at 7 months or so. That said, your discus do look stunted. Normally discus don't mature enough to breed till 9 months ( which is early) but normally around 12 months old. The one that can be seen clearly (the turq) has a very large eye to body ratio and the pointed head instead of rounded is another indicator.