There are even people making a career change in their late 40's, so it can be done. Not matter what your age, if you really want something, you are only going to end up older and still be wanting it if you don't pursue it. For some people happiness is more important than security or money.
However, you must be realistic about what you can expect out of flying as a career if you do attain it. Many people dream about becoming a pilot, but the reality is often not what they expect.
If you started now, then it will take a few years to get the ratings and time necessary to apply for a job. Figure at least three years to get rated and land a time building job to get the flight time required to meet regional minimums. Unless you do a $50K + 'academy program' with a guaranteed interview (no job guarantee, just an interview) then you can do it in 18-24 months. You can easily make Captain at a regional carrier and at 10-15 years seniority, you might see $80+k/yr as a regional RJ captain. You may very well get hired on at a major after a while, but you would be starting over again (pay cut, back on call).
You can expect to make less than $20K/yr for the first year pay, plus $2K or so each year after that depending on the carrier you get on with. Some carriers pay better than others. For example first year pay at Skywest is $18K but second jumps to $32K. Either way, you will have to suffer low wages for a bit, just how long is dependant on the carrier, they type aircraft assigned and how long it takes to upgrade. Upgrade, however, cannot be predicted with any accuracy. Upgrade all depends on pilot attrition, aircraft deliveries and airline expansion. Some carriers may have a 2 year upgrade now while others may have 7+ years.
The sacrifices you & your family (fiance) are going to have to make, financially & otherwise, cannot be underestimated. I don't want to be a "downer", but you really need to be educated on all that's involved to make an informed career changing & life altering decision. If you decide to 'go for it', do so with no illusions.
I made the jump in my 30's, and if I did not have a substantial sum saved and no loan debt other then my house, I cannot imagine how I'd get by. I know someone who had the money and did the PPL thru CFI at a flight school and in 3 years they were new hire F/O at age 46. Unfortuntely, at age 50 my friend has left aviation because of the low wages (expected top out pay/retirement) and BS at the regionals. They did not want to stick it out till 60. Three years on the line was enough to find out that doing it for a living was not really living their dream- even though they thought (and proclaimed) so in the beginning.
In addition, yours is a popular question at the message forums on these boards (Jetcareers even has a career changer forum):
www.jetcareers.com
http://forums.flightinfo.com