Stroud

There's a 1/2 marathon in Stroud next month. I could do it - do a lot more running between now and then and lose a load of weight to boot.
It's tempting.
Dropping people off for the Bristol half this morning I did feel a bit left out. I know I did a fairly long run yesterday - could I manage another 5 miles on top of that? I have 6 weeks to get up to speed.
It's doable...
Is there any reason why I shouldn't?
I can think of 100s frankly, but if I am serious about keeping up with the running and also with trying to shift a bit of flab before another birthday drags around, then it seems (at the moment, full of cake) like a good idea...