Poor vs career-minded? Aren't the poor more likely to be career-minded in order to improve their situation? These don't seem mutually-exclusive at all. I don't see why being poor makes it more likely for one to marry earlier, either.
My perception of poverty is that it's a transitional state, where people are interested in leaving it.
Depending on how poor they are, the transition may be slow, and to a rich person, they may only seem to be moving between different tiers of poverty, but that doesn't mean they aren't career-minded.
In particular, I would think that the poor vs the not-poor feel more need to delay marriage and family until they feel they can better afford it after having achieved long-term educational and career goals.
The poor tend to stick to labor jobs that you can train any healthy person to do in a few weeks on the job.
Have you spoken to anyone who dates these days? All the young men hate it. Women have all the leverage until they hit 28.