You have to be realistic and go into things with your eyes open.
I work as an air taxi pilot flying MEP. I went into this late in life and whilst I have been lucky to get a job, it barely pays the bills. I have a small retainer and then the rest is paid by the hour.
I am in my late thirties and with over a 1000 hours now, but my chances of moving into corporate or airlines look like being very slim. The preference seems to be "cadets" that work for very little and can be moulded easily to fit the company SOP's.
GA flying experience counts for very little these days, especially if you are older. Even the traditional recruiters of GA experienced pilots like flybe are moving towards mostly cadets. And with the stupid idiots out there that actually pay airlines to go to work as well, the chances for everyone are even less.
So yes, it can be done in you thirties, but as has been posted, well paid GA jobs are few and far between, especially ones that are salaried. I know of only one regional that still take a chance on over thirties, the rest, along with the charters and major airlines have unofficial age policies unless you have experience on type commensurate with age.
Personally, I am now looking to go back to my old job in IT, and possibly fly ad hoc or para dropping at weekends instead, as financially, it is no longer viable for me to chase a multi crew dream where the odds are so small.
I know there are people who will post of the great success of joe blogs who got an airline job at 42, but these are very small minority in a sea of twenty something 200 hour integrated students.
Sorry if I sound negative, but this is the reality of the situation for a late thirties GA pilot, so by all means give it a go if you have money to burn, but just be realistic about your career prospects ;-)