Nobody would suggest that engineers wait five years out of undergrad before attending graduate school, in order to better attain "life experience," and therefore be better engineers.
I see your point, but we have to remember that the arts constitute a unique situation.
The people I know who earned graduate degrees in engineering ended up earning $75K to over six figures almost imediately. On the other hand, I've known people who completed MFAs and then couldn't even get a decent job with benefits. Why? Because it's very difficult to get hired full-time on the skills of writing poems or short stories and maybe being able to discuss some 20th century American literature.
I know this sounds critical, but I speak from experience. I completed an MA in Spanish lit almost directly after undergrad (I took one year off) and then had to string various part-time jobs together for months before I landed any kind of stable employment. The reason for this was because my main qualifications were the ability to b.s. about literature and theory, and that was with the advantage of a second language. Having spent so much time in academia, I had almost no valid information about what was necessary to get a job in the outside world; I thought I could walk out with my MA and straight into an awesome, full-time teaching position somewhere. Ha! It has now taken me 2 years and lots of night school to earn educator certification and even hope to make a living wage, but at least I'll have something to fall back on after I do my MFA.
In summary (and I have posted this before), I would suggest to people who are seniors in college and contemplating going right into an MFA to consider how they will pay the bills afterword. If you have an undergraduate degree in something "marketable," then you will probably be ok. If not, then you might at least think about the possibility of taking some time off and exploring viable career options.
As someone else stated, grad school is not the real world. In grad school, everything you do is directed toward improving yourself and your own work. In the real world, everything you do is directed toward benefitting someone else: the company you work for; the students you teach; whoever. Having to hold down such a "selfless" job also teaches you higher standards of professionality and accountability, which can serve you well once you do go back to school. I have seen people go into all kinds of graduate programs just because it seems like a logical extension of undergrad, and it's easier to continue in academia than to venture into the unknown of the professional world. I think those who have spent some time working tend to have more appreciation for the graduate experience and may therefore get more out of it.
All this being said, I did in fact go into a grad program at age 23, so I'm not in a place to criticize the young people who plan to do the same. I'm only sharing my experience.