Here's one! I have been an avid mountain biker for over 30 years, though I'm much older/slower than I used to be.
I owned a couple of great Jamis Dakar bikes and during the era (circa 1990) of "less weight is better" custom built a titanium-framed ride that with one empty water bottle in its cage weighed under 20 lbs. I soon learned that less weight is not always good, but that is a long, boring story that did not end with any injuries except to the bike. I'm still riding it, but today it weighs closer to 25 lbs.
Since you have ridden in the past I won't remind you (oh yes I will) that you should start out with short trips, acclimate yourself to the bike, and especially the saddle (get the best one you can afford). Also, be mentally prepared for inevitable setbacks, ie. "I can't ride today as fast and as strong as I did last time out. Darnit!". Just be patient with yourself, keep pedaling, push through, and in a short time (even maybe the next ride) you will achieve a higher plateau of strength, speed, and bicycle shape.
And, then you'll get old and think to yourself, "Good Lord, what happened!" 
Enjoy your rides!
I changed my signature. The old one was too ridiculous.
Bookmarks