It's really not about age as much as it's about being mature, knowing what traits you want/need in a mate in life to choose the "right mate" for oneself.
The goal is to find someone who shares your same values, wants the same things for the marriage that you do, naturally agrees with you on how to obtain those things, and last but not least have a mutual depth of love and desire for one another.
Like attracts like and opposites attract divorce attorneys!
It also helps to be financially sound and have established a career path.
Being ready finding the right person is more important than one's age. However generally speaking for most people to figure out themselves well enough to know who they are and want they want, complete their education, and establish a career path to support marriage and family it's not uncommon for them to reach their late 20s or early 30s before being ready. Of course it all depends on what level of life the individual wants to live.
In my opinion choosing to bring children up in poverty crime infested environment is similar to child abuse. One should want to be the best possible position before starting a family.