I was 49 years old before I ran a GFA qualifying time (which I used to run the 2013 VLM) - after many years of believing I was 'not cut out' to achieve such a standard
I basically decided it was a 'priority' and trained hard (upped my mileage from a 'typical' 30-35 mpw to 55-70 mpw over a 12 month period prior to commencing an 18 week 'marathon specific' training schedule), ate healthily and generally made some other 'marathon specific' sacrifices (earlier nights for better/longer sleep, little/no alcohol etc) and bingo! - ran a sub 3:15 qualifying time (@ the inaugural Milton Keynes marathon in 2012) which i used to enter the 2013 VLM (subsequently running 02:59:05)
GFA can be acheived, take it from someone who thought it couldn't be - just takes a bit of time & sustained effort - then you're in!!