BTDT.
Got my motorcycle license and started riding late last year after my wife and I decided to do a Patagonia dual sport adventure for our honeymoon in late Feb.
Here's how I got started back in October:
http://forums.pelicanparts.com/bmw-r1100s-r1200s-tech-forum/1009515-old-bike-new-owner.html
The only real long distance I did before Patagonia was from San Jose to Los Angeles in 2 days at a leisurely pace, and then back in 1 day making sure to keep the pace up and stop times low. I was tired at the end of that trip, but never felt unsafe or uncomfortable. I actually just did it again a couple weeks ago.
Patagonia was 2000 miles over 2 weeks. Riding almost every single day. Some days were extremely cold, other days the food was pretty awful in some of the more remote areas. There were 3 days in the middle that were brutal, but overall it was very doable. I think I'm a little younger than you at 34 years old. I'm pretty active, skiing in the winter and mountain biking year-round + gym a few times a week. The hardest part for me was the cold. Even with heated grips and layering up with high quality gear it still gets to you. Also, if you're planning on getting off-road, you should be very comfortable with the dynamics and uncertainty of riding on dirt and how to handle the bikes. Also make sure you learn how to fall, I fell about 10 times on the Patagonia trip, mostly at low speeds. Before the trip I didn't do any off-road riding clinics because I had the mountain biking background, but I think I would've hurt myself if I didn't have that knowledge base and reflexes. So make sure you consider that. I've heard the BMW 2-day clinic is solid, but pricey.
Finally, we didn't have the proper bikes or knowledge base to do the route planning so we found a great mostly-all-inclusive package through rideadv called "The Patagonia Experience." They set everything up except for meals, and we had a great time at almost all the places we stayed at.
https://www.rideadv.com/motorcycle-tours/dual-sport-motorcycle-adventure-tours/fly-and-ride-the-patagonia-experience-motorcycle-tour-chile-argentina