so my question is, what's a reasonable expectation for how fast i should be able to do a 30-mile ride?
Well, that's not really what you want to know.
What you really,
really want to know is:
Am I riding as well and as fast I should be
for my age and the kind of time and effort I put into
my cycling and health routine?
Well, that's a good question. However, why would you ask strangers on the Internet to measure your performance if you haven't measured it yourself?
Off hand, I'd say you should be able go as fast as you rode last year. And I might add, you probably can't ride as fast as you would have if you would have tried as much at 50.
There's still time, still some chance that you can ride faster than you ever have in your life. But that depends on how fast you used to ride, and whether you can grip on what it takes to exercise for improvement, without the excuses.