If boys reach the first row before older people, they are more entitled to it

This is the view of some scholars, who say that it is
better for young boys to form rows behind the men. But this opinion
is subject to dispute. The more correct view is that if they get there
first, it is not permissible to make them sit further back. If they
reach the first or second row first, those who come after them should
not make them sit further back, because they got there first and that
gives them the right over those who did not get there first. So it is
not permissible to make them sit further back, because of the general
meaning of the ahaadeeth concerning this matter, and because making
them sit further back would put them off coming to the prayer and from
competing in that – and this is not appropriate. 

But if a group of people arrive together, because they
are traveling together or for some other reason, then the men should
form the first rows, the boys behind them, and the women – if there
are women present – should form rows behind them. This is when a group
is all together. But for older people who come later to make the youngsters
move and then take their places is not permissible, as we have mentioned. 

With regard to the hadeeth of the Prophet

(peace and blessings of Allaah be upon him): “Let there be behind me
those among you who are wise and mature” – this is meant to encourage
people who are wise and mature to hasten to the prayer and to be in
the forefront of the people. It does not mean that those who arrived
before them should be made to move for them, because that goes against
the shar’i evidence that we have mentioned.