you seem to be off to a great start. the challenge for many is to getem started. over feeding can be another. as for a their shell hardening. i've visited turtle trappers that had 15-16" shells with still their wood like textor. so it may vary. phantoms snapper looks like its beginning to occifie(harded up) and its what 7 yrs old. good luck with yours, their almost bulletproof.