I am also planning to fully dedicate myself to architecture after I finish my Chemistry degree. I am over halfway done my degree so I might as well finish it. By that time I will also be 23, which is still young! Arch school is only 3 years on average (I am from Canada) so there is still plenty of time to learn and grow in the profession. I feel like have a background in something other than architecture really enriches you as a person and allows you to see things/problems from another perspective. 

Best of luck with your studies.

The best time to enter is either when you are very young--early twenties-- when your body is capable of charettes and you are still naive enough to think there is something romantic and noble about being a starving artist, or else when you are old enough to have retired from some other line of work that actually paid you something so that you don't really need the money.  The worst time to enter is middle age.

i'm canadian as well, and I went into architecture school right out of highschool. my undergrad was 5 years (it was a co-op program), and i'm looking at a 2.5 year masters. Maybe it was because I was so young, but it took me at least 3 years to come into my own as a designer: to develop a style and truly understand the subtleties of architectural design - i am still building on this, of course, and i'm looking forward to my masters as a chance to further explore specific aspects of the profession in depth, now that i've got the basics of design, history, technology and construction. i question whether anyone without a creative background could throw themselves straight into a 3 year masters and really graduate on the same level as someone with both the undergrad and the masters (7 and a half years of architectural study, in my case) - having a background in something else does give you a unique perspective on things, but an architectural education is usually a well rounded one anyways. admittedly, going straight into architecture school is not for everyone - it's a grueling program which requires an immense amount of maturity, independence and focus (not the words i would use to describe most 18 years olds)... but a large number of people in my undergrad either took a year off first, or studied another discipline for a few years before switching their major. those are my thoughts. good luck! 

This is the kind of profession you do because you truly love it. Not for a paycheck. Architects work hard and often dont "make it" until very late in life. Consider the "Young Architects Award" designers get at 40. 

Regardless like clairemk said above, it takes time. And a lot of hard work. With reward for the very few.  But for me this is all worth it. 

^ People shouldn't pick architecture for the paycheck (it's not that big), but the paycheck's important. If someone's offering you work sans remuneration and chalking it up to a matter of passion you should run in the opposite direction. That is romanticism, and is probably easier to pull over on those with fewer responsibilities.

There is no ideal time though - it's completely personal. Many practice well into their senior years so late entrees are probably more common than other professions. I went in at 23, which turned out to be about average for my program. Some were there at 18, some at 30, and as far as I can tell there was little difference in success.

Ok. Good luck to all of you, whatever stage you're at.

About 100 years ago.