- definitely not too late; arch. is a field that has (perhaps more than most) a healthy share of older beginning practitioners, and you wouldn't even be considered remotely old anyway, you are still in your 20s!!  goodness gracious.  Arch is frequently a post-undergrad, or secondary career choice.  I wouldn't be surprised if it was actually a majority post-undergrad career choice.

- re: length of program... depends.  Do you actually hold a Bachelor's?   If so, you're most likely in for a 3 year M.Arch program.  I don't know of any 4-5 year M.Arch programs so I'm guessing you were looking at the 5 year B.Arch degree.  This is an excellent degree but unnecessary if you already hold a Bachelor's.  

- If you DON'T already hold a Bachelor's, and you want to be professionally licensed some day, then your fastest direct route to licensure is the 5 year professionally-accredited Bachelor of Architecture.  A longer route would be a regular 4 year Bachelor of Arts (or Science) in Architecture, + typically a 2 year Master's degree.  However, depending on whether you can get credit transfer for whatever college work you've already completed, this may be an economical option for you.  

- If you don't think you will need to be licensed some day, and, say, you want to economize cost (arch school is $$$!!!!), then just do a regular 4 year Bachelor of Arts (or Science) in Architecture and get a job somewhere.

- the post-degree period of internship (called IDP, for Internship Development Program) is essentially a period of enforced low wages while you supposedly get well-rounded experience in all the different parts of the profession required of a good practitioner.  (Although, to be fair, the low wages do continue after you are licensed, as well.  Ha!)  On paper, the number of experience hours you are required to document works out to be about 3 years.  In reality, the average amount of years it is taking people to complete this is 7 years.  (which in my case was spot on).  However, a good many architects get into the profession and realize that, for various reasons, they will not end up needing a license in their life-time, and that for them personally it's not worth pursuing.  So that's up to you.  All in all, I wouldn't let the length of the IDP period dissuade you from pursuing arch. if you like it.  IDP is really not that big a deal, despite the level of complaining it generates.  It's a pain, and there are good reasons to question its worth and legitimacy, and I for one wouldn't be at all saddened to see it completely done away with, but truthfully it is really not that big a deal.  There are much bigger annoyances in the profession than that one (such as competitions and free-laborers keeping profits and wages depressed...)

Hope this helps.

the thing I like about college girls is that the older I get, the more they stay the same

As a licensed architect, I urge you not to follow that dream. I recommend you do something else, that will not seem so "creative" but is necessary in our "service economy" of the 21st century in America.

Boring jobs at first, but are a vehicle for a nice life.

Go for it!  I was 24 (I was also in the middle age wise compared to many others).  That's only 4 years younger and - believe me - in the grand scheme of things, that's nothing.

I believe in doing work in something you love doing. And this applies even more in architecture, which you really, really need to love in order to make up for its shortcomings as a profession (relatively low pay, for one). If you were totally serious about it, my suggestion would be to immerse yourself in it. Along with preparing and researching getting into the school you want to go to, start reading books, magazines, and journals on architecture and design, start drawing and sketching buildings and urban scenery, write a blog, write about what patterns and ideas you can gleam in the city, etc. That is assuming you don't already do that. 

I also switched to architecture pretty late. I was in "community college hell" for a few years where it seemed I was taking forever to transfer and find what I wanted to do. I eventually decided on architecture back in 2007, my 4th year since high school graduation. I immersed myself in the field, read anything I could on architecture, joined the architecture club, and focused on the introductory architectural drawing and drafting classes I took in the beginning. After completing the courses required for transfer in 2 years, I transferred in Fall 2009 and finally graduated last May with a BA in Architecture at 26 years old. Now I'm in Beijing doing a one year internship for a local firm where I am actually getting some design work and will begin the preparation for applying to grad school when I come back home to SF early next year.

I might end up beginning grad school at 29-30 years old too. :)

be true to yourself... ask if you're really good in creativity, building, and everything architecture is involved in.  Are you in it because you hope to become a starchitect one day and make good money?  Are you good in drawing or are you did you just pick up a pencil to sketch recently etc?

Architecture requires real passion.. many drop out or switch fields because they realize the don't want to deal with all the stress, little pay, responsibilities, lack of skill in this competitive field etc.  

With that said, I'll be starting my masters when i'm turning 32, so you are far from old to get into this field.  I've had classmates who were in their late 30s and 40's during undergrad.

28 is not old for architecture school.  don't sweat it.

personally i don't think it requires a life dedication like some sort of religious conversion but it is not such an easy job either in spite of the effort it takes to get through the process and get a license.  we are notoriously weak in the face of business cycles and wages are not as high as you might hope. but hell what else is new?

entering m.arch school at the age of 28 was the best decision i've made in my life so far. u r not alone!

go for it!