Maturity is being able to disappoint an impulse without feeling deprived.

Not acting on an impulse used to feel like loss. At some point you notice you can want something, not have it, and be perfectly fine. That gap between the urge and the sense of deprivation is where most self-control actually lives, and it can be widened with practice.

Try sitting with a small want without satisfying it and observe what happens to the wanting. It usually fades faster than expected. The discovery that you can decline yourself something without suffering is worth more than any rule you might impose.