So, depending on how much of this decrease in violence with age is biological and how much is memetic, stopping aging (assuming it would lead to a large drop in the birth rate) may increase or decrease the total violence in the long run (as the chronological age of the population increases but its biological age decreases).
It would also depend on how anti-aging works. Suppose that every stage of life is made longer. If young male violence is mostly biological, then some young men would be violent for a few more years.
So, depending on how much of this decrease in violence with age is biological and how much is memetic, stopping aging (assuming it would lead to a large drop in the birth rate) may increase or decrease the total violence in the long run (as the chronological age of the population increases but its biological age decreases).
It would also depend on how anti-aging works. Suppose that every stage of life is made longer. If young male violence is mostly biological, then some young men would be violent for a few more years.