She raised him to be comfortable with his own urges.
My friend Mike (not his real name) had an enviable relationship with his mother. From when he was thirteen and she had caught him stroking his boner, she had, instead of getting mad, taken him aside later and talked to him about it. She supported his habit and even encouraged it.
When she first talked to him, she asked him if he shot white semen out yet. He said no, so she told him about how soon he would start producing sperm and how he would need to be able to clean up, and to tell her when he started so they could arrange how to handle the messes. One day, while jacking off, lying back on his bed one evening, his penis fired a single thin strand of cum onto his belly. Excitedly he called out for his mother, who came into his room. 'Look, mum!' he said. She looked at his penis lying prone on his stomach with the strand leading away from it, she smiled at him, left, then came back with a tissue and wiped the jizz up. First off his stomach, then she held his penis shaft with two fingers of one hand and wiped the head off with the tissue. Mike recalled that the unexpected touch made him moan softly with pleasure and another drop squeezed out which she also wiped away. She stood up straight again, looked around, and put the tissue in a nearby plastic shopping bag which she hung on his doorknob as she made her exit. Before closing the door behind her, she told him, 'Well Mike, you're a grown boy now,' and winked.
From this point on, he would clean up his ejaculations with a tissue (or just cum straight into the tissue) then throw it in a bag hanging on the door.
On the night before his 14th birthday, she gave him what she said was a special, secret birthday present, a bottle of sex lube which she said would help make his orgasms stronger. It did. He used it up very quickly. From that point on, she would get him lube on a semi-regular basis up until he was old enough to comfortably buy his own.
Her favorite word for an orgasm was a 'pop.' At breakfast on weekends, if he was in a really good mood, she'd even say something like 'good pop this morning?' In the car on the way back from school if he looked stressed out, she'd sometimes tell him, 'you really need to pop one as soon as we get home.' And when they got home, as soon as they were inside, she'd grin and tell him to have fun even as he eagerly ran straight to his room, close the door, and get down to business!
As he got older, he grew away from this openness, but she understood perfectly and didn't press the issue at all. But one day when he was 17, he had failed to close the door to his room completely. His mother entered, thinking nothing since the door wasn't shut. He was lying on his back, prone, with his rigid penis in hand, holding still. He was mere seconds away from his climax. Her eyes widened a little bit then she told him, 'Mike, dinner is ready.' He was already on the brink, and at this point was in no position to care about his privacy. He grunted, 'just a sec, mum' then gasped, heaved, and a large load began to issue across his chest and belly. She stood there and watched his ejaculation, bemused, from the first strong shots to the weak after dribbles. He relaxed, released his penis which lay still on his belly with his cum, and looked at her. She gave a giggle, smiled, and told him, 'you're still my son, I see!' She walked up, still smiling, and said, 'Nice pop! That's a big mess!' What she did next surprised him. She said, 'You must have needed that,' then reached out, ran her fingers lightly across his reddened balls, then lifted his scrotum and cupped the balls lightly between her fingers and chuckled, and said, 'These must feel a lot better now.'
Then she released his balls, grabbed the box of tissues from the bedside, handed him some and pulled some out herself and they wiped up the semen together.
From that point on, their relationship opened up again and to this day, they are still as open with each other today as when he was a child.