Congratulations on the weight loss, and keep it up. You'll manage the century!
Our local cycling community just lost a really special guy to cancer who had been over 300lbs in his 40's. He was told by his doc that he better make a change or he'd be dead in three years. He started riding a bike, quit drinking, lost the weight, and became something of a legendary figure in the cycling community for over 20 years. He did dozens and dozens of charity rides, raised huge amounts of money, helped untold scores of new riders train for their first big charity events, convinced them that they could do what they thought was impossible.
Anyway, if you'd met him, he'd have told you you could do it and you'd have believed him. So enjoy your training, keep it up, and have a fabulous, fun century!