My two cents..

Younger people must not be quick to rebuke older people. Instead, they must first exhort them and appeal to them, as they would to their parents. But if they persist on sinning and need to be rebuked, a younger person may rebuke without using sharp words, for those are appropriate to disciplining young stubborn people.

However, I don’t think it is wrong for a young man to sharply rebuke a stubborn congregation that includes both the the young and the elderly, as long as he is speaking to all of them in general and not specifically to older people only. I think a good example of this would be St. Paul saying “Foolish Galatians!” to the Galatian Church, which surely contains older people as well.