Congratulations on the weight loss! That's great. I am a neophite at riding too but I ride three to four times a week and started out this summer by riding 12-15 miles each time and then on one day I would add about ten percent to my longest distance. Two weeks ago I made my longest ride ever of 53 miles and felt great when I finished.
Just ride and keep stretching your limits and soon you'll be amazed at how much you look forward to a quick 25-30 mile ride.
Good luck.