Ive been pondering the idea of age, at which point I have two hypothesis about how I would advise those looking for an LTR/family, and likely how I will guide my boys...
1. Both sexes should limit the gap to 5-10 years. Obviously, this is not hard science, but good as a general rule. When you cross the 10 year age gap, you start to have dramatic differences in common interests, and also likely dramatic differences due to upbringing. For example, many kids born in the last 10 years are inundated with social media and technology, the previous 10 years? Not so much. This creates dramatically different psychological and behavioral hurdles for a couple with 10+ age difference to overcome. I'm not saying it can't happen, it's more of a question of risk management.
2. Men should date younger and wait for LTRs till they are 30 or later. In your 20s, you have one thing on your mind, and that is getting your d1ck wet. That and getting out from under the wings of your parents. In their 20s, men should build their wealth (e.g. assets, pay, social networks, etc.), travel, and build their mind through education (not necessarily college) and experience. Women can be an enormous distraction, which could prevent a man from pursuing his goals or getting saddled down with a kid. Also, by following these tactics through their formational years, the ideas behind abundance, purpose, and women can become further entrenched in the psyche.
Ideally, a 30-40 year old man finds a partner 6-10 years younger who is willing to hop on a speeding rocket of success.