I'm going to detract a bit from the advice given & advise you to wait. Your running injury needs rest & you won't get any while you're training. Things don't heal so quickly as we age. I just turned 56 and I've been biking for 20 years, so I have a little experience in nagging injuries

I would work on swimming, rehabbing your Achilles and improving your aerobic capacity by biking. Aim for something next year. Just my $.02.