In Megaburg all rats are equal, in terms of rights, but what in the end allows a rat to be heard or seen is their power (such as wealth). Gender does not play a role in deciding who can perform which job or hold a specific title.
Children of Mega Burg are not given any form of education (unless their parents grant it to them or they seek it themselves). The harsh realities of Mega Burg dawn on the younglings ever sooner and some established craftsmen, merchants or specialists of other professions offer something akin to apprenticeships, so that new rats can gain the necessary knowledge and experience to survive. These apprenticeships are usually unpaid.
In broad terms there are three castes of rats. The workers, who are of the lowest caste, and form the bulk of Mega Burg population. These are rats who get by from one day to the next. Gatherers, scrappers, looters, small-time farmers, handlers. Any job that does not call for any specialized education lands in this caste.
The middle caste, as you may guess, are those who are “specialized” in some manner. Skilled workers. Any craftsmen, warriors, artists and philosophers would be in this caste. They tend to be richer than the lower caste rats, although much depends on whether somebody is prepared to hire skilled workers at the time.
The high caste is reserved, in the eyes of rats, to those who hold the actual power, in some form. While seekers can be viewed as merely merchants they tend to go out of their way to hold enough influence to be more than just mere peddlers. Elders are the dominant example of higher caste rats.
While there is nothing stopping rats from different castes to “marry” it is usually hard for a rat from a lower caste to be considered a higher caste rat, just through having a suitably powerful mate. Marriage, as such, does not exist in Mega Burg, but rats do form bonds with each other. Since there is no formal institution upholding or regulating marriages polygamy is possible, if very costly since the rat would have to keep his many mates fed and happy.