Welcome Ryan. I too am new to mountain biking and just as Jeremy said it is quite addictive. I am in a very similar situation to yours, 36 years old, 2 kids, and married for 9 years to a wife I could not live without. Taking my 6 year old boy to football practice kind of gave me some motivation to get in better shape. He is fit as a fiddle and I was 200# at 5’8" tall.
I started back riding my bike around the ATV trails on my farm and on the road. When I first started back riding (about 3 or 4 weeks ago) I would ride about 20 minutes and be completely exhausted. After riding almost every day since then I have increased my time to 50 minutes and I am not exhausted at all. I can’t get enough of it, just don’t have much more time than that to ride.
Also I have shed 11 pounds since I started, down to 189 now.
Stephen