To the OP- one thing I haven't seen mentioned here yet- you should get your doc to check you out. Make sure there's no underlying conditions that might be aggravated by a sudden increase in cardio actvitiy- no blockages, etc.

Back when I started again (2004), there was a 15 mile loop I swore I'd conquer. I had to do it in 5 mile chuncks, with a 10-15 minute break after each chunk. Now, a 15 mile ride is just a good warmup.

You're going to amaze yourself... welcome aboard, looking forward to following your progress!