I used a HRM a lot when I was running, also a polar watch, and I'm 31 so close enough for comparison. Over a 50 minute 10k (I'm not a fast runner!), I'd average somewhere around 160bpm, with a max around 185bpm. I guess my HR could go higher, but I don't usually push the pain barrier!
I recently stuck it on during a 50 mile ride, out of curiosity. My average was more like 125bpm, with a max around 150bpm (guess it would go a fair bit higher if I'd thrown in an evil hill or two, though). I didn't push it, just rode at regular pace, which for me is 15-16mph average (I'm not a particularly fast cyclist either!).
Anyway, your numbers are more or less in line with my running values, so I'd say it's a perfectly safe HR to exercise at.
If I was going to be sustaining the effort for more than 2 hours (which is pretty much always the case on a weekend ride for me), I'd look to bring your HR down a little and work on building your endurance at lower effort. Spinning a slightly lower gear at a slightly higher cadence (aim for ~90rpm) is good for this.
It's easy to get pre-occupied with these (and all sorts of other) numbers when "training".... the best advice I can give is to get out on the bike as much as you can, maybe push yourself to slightly longer distances, and above all to enjoy your cycling! The speed and fitness will come as a natural by-product (until you plateau like I have - but then again I'm perfectly happy with where I am right now).
