There isn't one. Both in 2004 and today, the idea of marriage in the secular sense has a debatable value proposition. A lot of marriages fail. Divorce is the most common definition of failure.
Based on a variety of social science statistics, there's about an 80% chance that a marriage that has started since the 1990s will experience AT LEAST ONE of the following 3 things:
1. Divorce
2. Infidelity
3. Extended periods of severe unhappiness, where the relationship seems to go on and on based on inertia and not actual joy.
Marriage doesn't work for a lot of people.
@Zimbabwe is correct about how marriage once was. To the outsider, a lot of married people look ok and it confers some social status. On the inside, things are rarely as good as they seem. I think marriage works best for a small subset of devout religious people and works less for more secular people. On SoSuave, a large portion of forum participants are seducers who are not devoutly religious people. For the SoSuave audience, marriage isn't an ideal proposition.
Age at first marriage has crept up since 2004 when this was originally posted. The average/median figures are around 30-31 for men and 28-29 for women.
There is an argument to be made for locking down a good prospect before she rides the carousel. The carousel was not as vicious in 1998-2004 as it was in 2010 and later.
A lower partner count can help with having things last.
There's a good probability that the 20 year old discussed in 2004 is now a 37 year old woman with a high notch count and possibly a single mom.
Would I have put a ring on a 20 year old in 2004? I turned 21 in 2004 and I had no plans to do so at that time. I had one wild girlfriend who was 19 then for a period in 2004 and a few other casual bangs that year. I was thinking solely about the sex then. Sex is still important to the mid to late 30s me of the last 5 years but my sex drive has diminished since then although it is still healthy. I notice that I am not as well balanced mentally and emotionally if I go too long without sex.
A lot of men put a ring on it hoping to lock down sexual frequency for a long time. It doesn't often happen like that in reality. Marital sex is regular in the earlier years of a marriage IF there hasn't been too long of a pre-marital period (~2 years pre-marital). After 3-5 years of marriage, sex frequency is not that high. It must be noted that non-marital relationships see sex frequency declines by the end of 5 years together in a lot of cases. The passage of time is a relationship is the key variable, not the legal status of the relationship.
Relationship games and drama do not end with the wedding ceremony. The early stages of a relationship has the most game playing and it takes more effort to form a relationship than maintain it. Jay was correct about letting your guard down. There are dangers with that too, mainly in the form of divorce. Female infidelity has become more common since the 1980s, which is when the Sexual Revolution of the late 1960s became fully mainstream.
Both married men and married women are guilty at times of letting their guard down, gaining weight, and becoming unattractive.
Part of the reason I've kept my BMI under 25 and stayed in reasonably good shape is that I've never perceived great security in any of my relationships. I've never married. Married people get trapped into the illusion of marital security. If marriages were so secure, there would not be rampant divorce.
It is my hope that the original poster didn't go through with a marriage in 2004-05. If he did, it most likely didn't work out. It would be good to see an update from the poster about it.