What would you like to do??
Is the full a possibility for you? If so, I would recommend that you get a couple of halves under your belt before taking on the marathon. Marathon training is one of the most taxing events you will place on your body and it isn't for everyone. If you never run a marathon, that does not make you any less of a runner than those who crank out one a month (something I find VERY irresponsible, by the way). The inflammation from the training alone may lead to issues. I'm not saying you should not do one, just remember that you will need to allow for wiggle room in your training and allow for lots of recovery time, especially as a master runner. Recovery is slower--just due to our age alone, not to mention the other stressors in our lives.
I am almost 6 years into my running career and I must confess that I have decided that having the ability to run far exceeds any PRs for me. I am blessed to be running and have been injury free for the most part...I have had my fair share of minor aches, but I have never experienced an injury that left me side-lined for more than a week.
I wish you well with your decision!
RUN SPARK STRONG!