Hi Andy.
I just turned 32 at the end of January.
Essentially I started back running in January '07 (used to run as a kid, but gave up just before turning 17). I was very overweight when I started, but the initial weight loss was quite quick. I ran my first HM after 6 weeks (1:34), another one 6 weeks later (1:28), and after the second one thought that if I was going to do it I should do it properly and joined a club around the end of April/start of May. Then I started to build up the mileage a bit and ran the New Forest Marathon in Sept (2:55). I finished out the year with a 10k pb of 36:40, HM of 1:23:35 and Mara of 2:55:46.
During my first year of running I realised that I can manage a reasonably high level of mileage (peak week for the year was just over 128, average was 48 - first couple of months were low, hence why the average was lower, the average for the 3 months before my first mara was ~70 I think). I also realised that within my club I am viewed as a bit of an oddity because I do a bit of mileage, so if you can are willing to do a reasonable amount of mileage and can manage it without getting injured you'll automatically have an advantage over a lot of club runners.
During my second year of running I got my 10k time down to 34:17, HM down to 74:17, and mara down to 2:35:48. This was down to consistently higher mileage, and later in the year, more structured training.
This is my third year of running. I have been plagued with problems so far this year unfortunately, though, I hasten to add, not typically linked to running. At the start of the year my main aim was to get down to sub-2:20 shape ahead of the Dublin Marathon in October. Whether that is possible depends on me getting a bit of a break luck-wise as I have been very unlucky so far. The key though to future advancement is consistently high mileage (am quite comfortable knocking out in advance of 110mpw) and good structure. As to how far can you go starting late? I really don't think, within reason, that age has much to do with it.
The sub-3 thread is littered with late starters who have gone further than me (marders and Marigold to name 2) and who I hope to emulate (and eventually pass).
Only advice I would give is train hard, don't put limits on yourself and see where it gets you.
Also, if you want to email me and ask anything else, feel free. I hope some of that helped.