For us men..lets be honest. It's better to get your kids between the ages of 20 and 40 instead of 40 and 60. It possible, I know..but..
Let's look at becoming a first time father at 40+ and what it entails for a man.
From a biological standpoint, we can impregnate women at that age. A 40 year old man's sperm quality is lower than his 25 or 30 year old self, but it's still good enough to cause pregnancy. Older sperm is more likely to contain deficiencies. The solution to this is to have a partner that is substantially younger. It is best for a 40 year old man to have a partner 10+ years younger if he's having kids at 40 to minimize chances of complicated pregnancies and birth defects. One of the few 40 year old men I know in-person who became a first time father had a wife who was 32 at the time of birth. 32 was 8 years younger, which is close to 10 and that's still borderline risky.
There are more practical lifestyle reasons why older fatherhood is less than ideal.
There are a couple of considerations around physical health.
An older man isn't as able to handle the physical rigors of infancy and toddlerhood as easily as a younger man. If there are nights where sleep quantity is reduced due to a child's needs, that's more difficult to cope with at 40 as compared to 25 or 30. That could affect his ability to do his job, which is an important consideration for a parent.
An older man isn't able to keep up with his younger child as easily. It's less than ideal for a 45-50 year old man to try to keep up with his 5-10 year old child or children. That impacts the memories that an older father can make with his children. It's nice for a father to be able to play sports with his son or daughter.
The biggest issue with a 40 year old man having a child becomes money and financial planning. When a 40 year old man has a child, he's not an empty nester until 58 (if that's his only child). If his child goes to college, he might at least partially fund that and the burden of that would extend to 62-63 years old. That will impact retirement planning. That also assumes that a man can retire on his own terms, which is a faulty assumption as I'll show below. However, even for men who are fortunate enough to retire on their own terms, having financially dependent children (even financially dependent adult children) after age 55-60 is not the wisest of financial decisions and can delay retirement.
Additionally, most men do not retire voluntarily. The majority of people experience involuntary retirement and that typically occurs somewhere between ages 50-65. For white collar workers, involuntary retirement takes on the form of job loss after 50 and the inability to get hired for similar white collar work after that. For blue collar workers, involuntary retirement takes on the form of a man who is physically unable to do his job due to injuries and overall physical condition. It's not good be to a 55 year old man with a 13 and 15 year old still at home when you're experiencing involuntary retirement.
Also realize that most men who get laid off during the 50-65 age range are also more likely to get divorced or dumped too. However, a man in his 50s who gets laid off and is forced into early retirement as likely to get divorced from his similarly aged wife because a 50 something woman has fewer options for longer term relationships out there. A man who is 25-44 years old who loses his job is a much higher risk candidate for dumping due to unemployment. Girlfriends are more likely to dump than wives. When a 32 year old man loses his job, his highly in-demand 30 year old girlfriend is far more likely to dump.
For the reasons above, I think it is best for men to have either have children or adopt children between ages 25-35. Men 25-35 are healthier and can raise them to adulthood without significant financial impact.
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