Years ago when I worked out regularly I used a Concept 2 as a warm-up. I once decided to got flat out for 2000m to see what I could do.
I managed 6'54" which according to the Concept 2 website gave me a world ranking of 124th in my age and weight category. 
I probably couldn't even sit on one now! 
Does that mean that my pb, 6'17" for 2000m, age 42, is pretty good then?
You probably shoudn't be wasting time on a bike and getting busy finding a rowing club:
My scale of 2k times:
8' decent time for a lady with a bit of training
7'-7'45'' lady club level rower
7'30'' decent time for a man with a bit of training
6'30 7'15'' man club level rower
Any time below this is impressive! I am not sure how lower you should be at 42. peak is probably at 35ish.
In the last few years I've used a CII rower in the gym over the winter months - just got back into it over the last few weeks and I'd forgotten how hard it is, especially as I didnt really do very much at all last winter.
A friend who is a pretty decent amateur rower told me almost exactly the same as the times outlined above eg 7m30s for 2000m is decent enough for somebody who's main sport isnt rowing. Also, he recommended an absolute max stroke rate of 25. I had previously been rowing a fixed time, aiming for 2m00s / 500m and gradually extending the time, starting at 15 mins and gradually exteding up to a max of 20 minutes.
I'm now doing 5000m regardless, managed just under 20m last week but wasnt exactly a picture of health after it - one of the disadvantages of a gym at work is that its your colleagues who can witness you suffering first hand!
