Sheikh `Abdul-Majeed Subh, a prominent Azharite scholar, states: “As far as Islamic Shari`ah is concerned, there is nothing wrong in proposing to a girl that has attained puberty after consulting her parents of course. However, generally speaking it is not preferable to have a long period in engagement because engagement in Islam is no more than a promise of marriage and therefore all ethics regarding relations between non-mahram persons of the opposite sex must be fulfilled, i.e. there should be no khalwah (illicit privacy) and the girl should be wearing hijab in his presence, etc.
I also prefer not to hasten to engage at a young age as it is likely that the girl or even the groom may change his or her mind.