Is one who comes forward to the front rows to fill a gap sinful, knowing that some elderly people are annoyed by this, even though joining shoulder to shoulder with the worshiper is a Sunnah?

Many scholars have permitted stepping over people's shoulders to fill a gap in the صف (row), whether or not there are other gaps, and whether the gap is near or far.

Al-Nawawi said: If it is someone other than the Imam, and he sees a gap in front of them that he cannot reach except by stepping over, then stepping over is not disliked, because those sitting behind it are negligent by leaving it.

Ibn Qudamah said: If he sees a gap that he cannot reach except by stepping over, he may step over. A person should enter as much as he can and not leave an empty space in front of him, for there is no sanctity for one who leaves an empty space in front of him and sits elsewhere.

However, care should be taken not to inconvenience the elderly. If there is a gap between the worshippers, you can sit behind the row until people stand up, then you can move forward to the row when people are straightening the rows.