I'm sure there are many of us out there - I'm the same as you. Last year I started biking to lose weight and get healthy. I was diagnosed with type 2 diabeties a year earlier and was in denial. The doc said he was going to give me more pills to take (and I was already taking 3 a day) and I would likely die of a heart attack before I was 40 (and I was already 35). I lost 30 lbs last summer biking and the doc backed off on more medicine. This year I am working to lose another 40 (got a late start last year).
Don't worry about what others say - are they on a bike? or out there doing it? If not - then they have no right to say anything - let them go back to their couch. They say things to make themselves feel better because they aren't out there doing it. If they are also bikers - shame on them - I bet they weren't in great shape when they started.
I watch the bikers when I'm out. There are fit and not so fit ones. I say hello to all I see. I'm sure the fit ones shake their head at me, the 250# guy on a road bike. But two days ago I held with a fit guy going up hill and on the flats for about 3 miles before he was able to pull away, and I let him go because I was going for distance, not speed.
Remember that, distance improves health more than speed. Try lower gears so you don't get out of breath. Your body needs oxygen to burn energy efficiently and provide long term supply - if you work too hard your body burns surgar and your muscles burn as well.
I did my first ever 20 mile ride with my mountain bike yesterday in the rain. It was great. I used the mountian bike because it was raining and wouldn't dare take my road bike out in that so I didn't plan on going that far. But I felt good, kept an even pace and took the hills slowly. I was a little tired last night and still a bit this morning, but the accomplishment was worth it. And I was surprised it only took be an hour and a half (6:30 - 8:00pm)
So hang in there. You have decided to try something you'll really enjoy - I do. And some day you can give those just starting out encouragement as you pull up next to them, and ride along with them for a while before speeding on along your route.
Mark
'01 GF Tassajara
'03 LS Blue Ridge