upping the distance.

If you are really motivated, able to honestly assess what it will take, and willing to stick with it, then it's absolutely doable. Good way to celebrate turning 50. Building it up over 4 years sounds like a sensible approach.

As already stated, getting in more miles on the bike would be a good way to start. On the bike you can put in a lot of time without hurting your body from the pounding. Perhaps create some motivation by signing up for some of the great sportive rides that can be found around your neck of the woods. They are good ways to get you used to riding longer distances. Check out cyclosport.org for a great resource for doing longer distance rides.

I noticed in one of your race reports that you mentioned that you were really tired after the swim leg. You'll likely find that some swim technique training could make this a whole lot easier, and at a higher pace. If the swim is a real struggle at 3+ min per 100m then you probably stand to gain a lot simply by working on form and relaxation in the water, even before you worry about fitness gains.

Good luck.

Thanks for taking the  time to reply and the tips you've given.  I have been aware that I don't  do enough on the bike. I have a mountain bike and a trek entry level racing bike (which has helped me speed up without any extra fitness.) I am that I am a bit scared of road traffic, but that's not a very ironman attitude is it??  And I am becoming increasingly aware how important the right can do attitude is for triathlon.

SO, I'll just have to get on and do it..and see how far I get. Thanks again. I just needed people to say - yes you can do it.