It is permissible to marry a young girl. However, there are two views on whether intercourse is permissiable. One view says they can have intercourse if she reaches the age of 9, while another view says intercourse should not happen before she is ready for it, and this seems to be the majority view of Hanafi, Maliki, and Shafi'i schools of though.

> The fact that it is permissible to marry a young girl does not mean
> that it is permissible to have intercourse with her; rather that
> should not be done until she is able for it. For that reason the
> Prophet (peace and blessings of Allaah be upon him) delayed the
> consummation of his marriage to ‘Aa’ishah. Al-Nawawi said: With regard
> to the wedding-party of a young married girl at the time of
> consummating the marriage, if the husband and the guardian of the girl
> agree upon something that will not cause harm to the young girl, then
> that may be done. If they disagree, then Ahmad and Abu ‘Ubayd say that
> once a girl reaches the age of nine then the marriage may be
> consummated even without her consent, but that does not apply in the
> case of who is younger. Maalik, al-Shaafa’i and Abu Haneefah said: the
> marriage may be consummated when the girl is able for intercourse,
> which varies from one girl to another, so no age limit can be set.
> This is the correct view. There is nothing in the hadeeth of ‘Aa’ishah
> to set an age limit, or to forbid that in the case of a girl who is
> able for it before the age of nine, or to allow it in the case of a
> girl who is not able for it and has reached the age of nine.
> Al-Dawoodi said: ‘Aa’ishah (may Allaah be pleased with her) was
> reached physical maturity (at the time when her marriage was
> consummated).
> 
> It should be noted that al-Shaafa’i and his companions said: It is
> preferable for fathers and grandfathers not to marry off a virgin
> until she reaches the age of puberty and they ask her permission, lest
> she end up in a marriage that she dislikes. What they said does not go
> against the hadeeth of ‘Aa’ishah, because what they meant is that they
> should not marry her off before she reaches puberty if there is no
> obvious interest to be served that they fear will be missed out on if
> they delay it, as in the hadeeth of ‘Aa’ishah. In that case it is
> preferable to go ahead with the marriage because the father is
> enjoined to take care of his child’s interests and not to let a good
> opportunity slip away.

Source: https://islamqa.info/en/answers/22442/on-acting-and-the-ruling-on-marrying-young-girls