What difference is pointed out by the author between the young men of his generation and the young men of the new generation ?

The narrator, J., points out the difference between the new generation and his generation.

When the old boatsmen narrates false or at least exaggerated stories about their achievement- long expenditures on a sculling boat, the young men of J's generation believe them and awe on the strongness and the determination of their elders.

In contrast, when J and his companions tell such anecdotes to the young men of the new generation, the boys laugh at them and exclaim that they were lying and spreading false stories.

I hope you understood, and please excuse me for my mistakes, if there are any. Thanks