Well hiking difficulty of course depends upon the terrain. How steep and or narrow the trails are, and the difficulty of footing. If the terrain is difficult you want to transport your pup in a backpack carrier.
So like others said start out with just walking your dog for 30 minutes and see how they do. It is not just their cardiovascular fitness, but also their paws need to toughen up as well.
Razzle at 9mths old or so went on a 4-5 hour hike - relatively flat terrain - we stopped for lunch and a swim, and completed the hike. First time I had ever actually seen him tired! But by the time we drove back to the cottage 20-25 minutes later he was raring to go again.
