What madscott said.

I don't know how Audax rides operate in Europe, in the states we call the equivalent rides brevets. At least here in the US, the general philosophy is to go at your own pace, and as long as you make the checkpoints in time you're fine.

In Audax rides, are you generally expected to ride as a group, or is it OK to do the ride on your own?

If it's the latter, and if you feel OK about riding alone, then I'd say go for it. You might meet people who ride at your pace and you wouldn't be alone after all.

(btw, I did my first brevet ride at age 47 )