A question for the OP and others who say masturbation is completely healthy and not immoral:
Is there ever a point that masturbation becomes immoral and destructive? Is daily masturbation wrong? What about every hour? What about mastuebation while using porn? What about while fantasizing someone in a lustful way?
I ask this precisely because, often, we want to say masturbation is not a sin because we are thinking of the strong urge of the adolescent who can’t control his hormones. We think it isn’t fair to scare young people into hell and to hate their sexuality. And granted, these are good insights.
But precisely it misses the fuller Catholic understanding of sin! Mortal sin must take into account the subjective experience of the individual. Masrurbation is inherently disordered precisely because we weren’t given our sexual organs in order to please ourselves. Sexuality is fully expressed in marriage, ordered to new life.
So we want to avoid the extreme of saying that each time some commits masturbation, they are also committing a subjective mortal sin. That’s not necessarily true.
However, I think that digging deeper will show that the only consistent view is to say that masturbation is, in itself, disordered and misses the mark of sexuality.