My arms have always been a bit ahead of everything else when it comes to development.
I only did two sets a week for a while.
Just started doing them again.
For abs I do this:
Monday - 3 sets of crunches to failure
Tuesday - 3 sets of hanging leg raises to failure
Wednesday - 3 sets of ab ball to failure
Then I repeat for Thursday, Friday and one day on the weekend.
Getting older sucks. Its hard not to gain weight!!!!