My papa tell me say for their time, before you reach 25, you done already marry or about to. But today, 30 self never put marriage as priority. Plenty good reasons dey sha o but some their reasons no reason enough to be single at certain age.
Maybe in Southern part. Go to North and see the difference. It has been estimated that by 2050, Nigeria population could surpass 1 billion if they continue to reproduce the way they are reproducing and nothing changed till now. More population are coming from the Northern part and they marry fast. Especially their females.
In the South, check those that just passed though senior secondary school and never go university, or those that did not go to secondary school at all. You will noticed they they marry fast.
In the North, as many of them get educated, many more do not get educated like people in the South.
Southerners do not marry and give birth fast again like the Northerners do.
Education is somehow related to this.
You are right, I no actually put the Norther Nigeria into consideration. Their custom and tradition actually makes early marriage easier. However, I no too cherish the pace they are going in terms of population that is not well taken care of... these are the outcome of their marriage system.