First, tell me what country you are in. Assuming you are in developed country. Probably a master degree is what you need.

And then,

It is absolutely not too late. You will need to get a masters degree if you want to become a licensed architect in the US. But age 25 is so young, my good friend the famous architect Rick Joy did not start architecture school until he was 30! You have plenty of time. Spend a year or even two doing some research into what school programs would be the best fit. Good luck!

no, not at all. you may have to make some changes to your lifestyle and manage your expectations about income to get it all to fit - but you can find a way as long as you are careful to avoid taking on too much debt for education. do ignore all the people who complain bitterly about the career online. for most of us, it's a decent middle class career.

Create a portfolio and go school.

Not too late, at 42 I decided to go for the full meal deal too.   Its never too late to better yourself

(Assuming you're in the US)

It's not uncommon for people to go for an M.Arch with no undergraduate design experience. Most programs have two (or more) tracks, at least one for students without an architecture background. It's most likely going to be a ~3 year degree.

I started grad school at 26, finished at 28, and I was just above the median age. Plenty of classmates in their early 30s. You're definitely not too old. If anything, having a bit more life experience under your belt has given you a better work ethic and will make you a better student.

I was a little older than you when I decided to go back to school for architecture, and was 28ish when I got my first full time job in architecture. It was the best decision I ever made.

I was 25 when I started grad school. It's not too late. I felt like I was slightly older, but in reality it wasn't an issue at all. There were plenty younger than me, but also plenty older than me. I only needed 2 years to complete my M.Arch (because I had a bachelors in architecture), you'll likely need 3 years. That's really not that big of a deal.

Lots of good advice above but I'll add in that you don't need to go to one of the top programs or private schools to become an architect. If cost is a concern, look at your state university (universities) and see if they have a NAAB-accredited M.Arch program. Don't pay out-of-state tuition unless there is no other option. As tduds pointed out, check to see if they have a track or program for students with a bachelor degree in a subject outside the field of architecture or design. Some schools call this an M.Arch I, some call it an M.Arch III or M.Arch Track III, others just refer to it as a 3-year program. What it's called is less important than making sure it is NAAB-accredited so you can use it to become licensed* (my school had a MS.Arch program that confused some applicants who didn't know better). 

Also, don't believe the schools if they tell you that you won't be able to hold a job and complete the program. You can work and go to school at the same time and there are plenty of people on these forums who can share their experiences and what worked for them. You may not be able to earn enough to pay for tuition entirely without loans, but you can make up a lot of the difference if you want to. Don't take out more loans than you absolutely have to and even then, don't do it if you won't be able to get a job to cover the cost of the loans. Again, there are other threads here that talk about realistic expectations for salaries upon graduation in various cities and regions as well as the Archinect Salary Poll which you can use to get an idea of what a salary might be for you.

Also, if you haven't been looking at NCARB you might as well get started navigating their website. They have some helpful information that describes the most typical pathway to licensure (1. Education, 2. Experience, 3. Examination). NCARB manages the process for logging experience (AXP) and examination (ARE). 

*Technically speaking you don't have to have an accredited degree in all jurisdictions to get licensed and practice as an architect, but all jurisdictions have a pathway that include a NAAB-accredited degree so it gives you the most options. You can view various requirements using NCARB's website, but don't take what you find there as definitive. There are usually some issues with the data and you should always verify requirements with your specific jurisdiction if you have any questions.

E_A, explained this well. 

Gelie, depending on where you are, the state you are in or even a nearby state may have alternative paths to licensure that doesn't even require a degree. However, getting jobs in architecture is slim without some architecture-related education be it a 4 year BA/BS degree or an NAAB accredited degree. With your existing education, gelie, you would likely need to take the ~3 year M.Arch curriculum for a NAAB accredited degree because of your prior bachelor's degree in business. Doing this would cost some money given the cost of tuition for graduate-level degrees but getting that M.Arch will serve you in meeting the education requirements of most jobs posted. Your business education can be of use later in your career when you establish your own business (if you so choose) or if you become a principal of a firm because of the knowledge in business management because that is really what principals of firms tend to do more than they are necessarily designing.  

Hi I am currently looking to enrol into a university in Australia for an architecture undergraduate course. 

I am 28 and I know it is quite late to start studying but I don't want to regret not going for it later.. 
However, before I begin, I would like to know if it is mandatory to study 5-11 years. Is a bachelor's degree from a Architecture major insufficient to get a job? 

Not too late at all. Look for 3-year professional Master of Architecture programs that are designed for those with no previous experience. In my experience, these programs oftentimes produce the most interesting cohorts because you get such a wide range of previous academic, professional, and life experiences all being introduced to the world of architecture, design, and the built environment at the same time. That range of backgrounds helps shape some really interesting design work and design conversations. Here's a little insight into what it's like: No Previous Experience Necessary

You can go the M.ARCH route and design/draft technical construction document sets for a design-oriented firm. While I agree candidates with a mix experiences, can come up with interesting design work, economics plays a big role in each project.  That's why most work design-oriented offices, have projects that go into archive and never see the light of day, but hey its fun.

You can pursue a degree in, a Masters Real Estate Development 1 - 2 Year Program. You will be part of the execution of planning a project, hiring the architect, figuring out financial models, etc. The conversation is from vision to tenant occupation. However, you won't be designing the project, but will definitely be having dialogue with your architect to be on time and budget. Plus this route you make 35% higher salary, without being on a computer all day.