Hey man, awesome news! I've been a cyclist for a while now - I did a ton of mountain biking as a kid, but I bought my first road bike in 2007 after moving to Boston and not really being able to easily get on dirt. Got increasingly serious about it, and ended up riding the Pan Mass Challenge (two day Jimmy Fund/Dana Faber fund raiser, 110 miles on day 1 and 82 on day 2) in 2012. I wasn't going to do it in 2013 anyway but I ended up tearing my ACL that spring which set me back (and essentially undid all the fitness I'd been working up prior to that, lol), but got back into it last season, and cumulated with a 120-miler from Boston to Provincetown on the tip of the Cape with a few of my riding buddies.
This year we're doing a 170-mile two day (100/70) MS fundraiser (one of my riding buddies has a cousin who just lost her mother to MS), and doing that P-town ride again, so now that there aren't 10 feet of snow on the ground I've been getting out there and trying to work off the winter weight.
I'm about 6', and peaked out about 205 this winter (all time high for me) so I'm trying to get back down to about 185, which is what I weighted at the end of the summer I rode the PMC. I'm down to the mid-high 190s and the riding season's only really getting started out here in Boston. The big thing for me is while my diet actually isn't all that bad, I unquestionably drink a bit too much, which has been keeping my blood sugar a little higher than it should be and cholesterol somewhat elevated for my age. Even just some modest tapering off - say, not having a beer or two with dinner most nights - has probably made a difference, and as I start riding more I should speed things up somewhat too.
That's a pretty good pace, man - sustaining 17 for a 30 miler isnt bad at all. I think I have a little more in the way of hills than you do out here - Boston itself is pretty flat, but I grew up in the northern Berkshires so I usually ride Mt. Greylock a couple times a summer. From my parents' place to the summit is about total elevation gain of 3,500 feet or so (gross - net is about 2k) over 33 miles, and the mountain itself is probably an average of about 8% grade once you start the main ascent, but peaks out in 14-15% in places. It's BRUTAL.
You basically just have to grunt it out in your granny gear, and no matter how many times you do it, it never gets any easier - it hurts just as much, but you go from like a 4mph pace to maybe a 6-8.