Actually it seems to me the current Christian fad is short engagements and marrying young. And I disagree with that for the most part. (Especially the marrying young part, not so much the short engagements.)
But I also disagree with the society fad of long open ended engagements and waiting forever to get married.
Now to address your question
If I could go back and change my life, I would not date until it could progress (it would have saved me a lot of heartache and saved me from many mistakes and issues that I have had to and still have to deal with) to the next step and I hate how society has somehow changed the age to mid 20's for marriage. Why is this?
Multiple reasons. . . increasing lifespans and increasing educational needs for both men and women. The increasing educational needs more then anything.
I do agree that there has been a maturity change in which the level of maturity that used to be expected from someone aged 20 is not expected until later in life. This has a lot to do with the educational requirements. But there are other factors, the job market is fairly limited to the young and parents now have the resources to help their children through school more.
Plus I think our parent's generation has become a bit of a me-first generation and that was passed on to us as their children. This to me is westernized individualism taken too far. Sacrificing for the greater good is has not died out but has been far more limited in people's minds since the 60's.
Some number of years ago at the age of 20 I would already be married and have a child.
See this is where Christians tend to over emphasis something and thats exactly what you are doing.
Median Age at First Marriage, 1890–2010 — Infoplease.com
Even in 1890 the median age at which women married was 22 and since then has gone up 4 years to 26.
For men however its only gone up from 26 to 28.
The big reason as to why women has gone up 4 years and men only 2 was because that now women are expected to put together careers before they get married. Prior to that it was just men who where expected to do that.
But really the age of first marriage has not changed
THAT MUCH considering 1890 was 120 years ago. 2 years for men, 4 for women.
Throw that in with the fact that lifespans from that era and earlier where at least 30 years shorter on average then they are now.
http://www.efmoody.com/estate/lifeexpectancy.html
In fact its interesting to look at
Age at first marriage percent change (1900 to 2010) - Some rounding involved
Men: 7.7%
Women: 18.2%
Life Expectency Percent change (1900 to 1997) - The 2010 percentage would only be larger. Some rounding involved again.
Men: 53.7%
Women: 56.6%
Really the bolded part is something that so many people seem to ignore in this sort of conversation. We throw around immaturity which may in part be true. And we also throw out there education which is true. And careers I see a lot too which is also true. But for both men and women the average life expectency is over 50% longer then it used to be while the age at first marriage change has been a paultry 7.7% and 18.2% change. This is highly important because if you are only expecting to live to 47 or 50 then you might want to get started on the making babies a little bit sooner then if you can expect to live to be 73 or 79 years old. Hence if there is more pressure to get started on children then there is obviously a reason to get married sooner rather then later.
In short perhaps the biggest change is that people in modern America can reasonably expect a full 30 years of extra lifetime. It used to be that the greast pressure was having the children and raising them to adulthood before you died. Now the greatest pressure is having children before the woman hits menopause. Huge difference. . . a woman in 1900 would not have wanted to have a child at 35 because in all likelyhood she may not live to see him/her out of the house and on his/her own. However if a woman is still able to have children at 35 then there is no problem with that because living til nearly 80 she can expect that her child will be 45 or more years old by the time she dies!!! Enough time to not only see him out of the house but see her grandchildren become teenagers or young adults! Maybe even enough time to see great grandchildren! In fact I know of at least two living women (one of them my grandmother) who have great grandchildren now. Something that would have been nearly unheard of in 1900.