At the advice of our vets and friends here on the board who have been hiking with dogs for years, we waited until our Lab was about 18 months old before she started tackling steeper trails.
Starting out, begin with modest days and gradually work your dog's range.
Remember, they'll want to please and you may not seen signs of strain. Bring water and food for your dog. You might want to avoid really rocky terrain and trails until Colden's pads have toughened up. After being out often for the last year, Boo's pads are like a combination of leather and sandpaper.
Watch the warmer days. Dogs don't sweat, they stay cool through their tongue, and on hot Spring or Summer days, they can overheat.
Enjoy your canine companion.
Not everyone loves dogs. Be sure you teach Colden good trail manners. I carry a short leash across my shoulders like a bandolier. When we're on trail, I'll usually leash Boo and make her sit at heel just off to the side of the trail and let hikers pass. I also try to leash her if there are other dogs in the woods unless I'm sure they will make friends.
Labs are food hounds. My dog is a shameless beggar so I try and leash her to me or to a tree during lunch so she doesn't pester other hikers.
(I suffered a lapse this winter. Was hiking with Dick and he had his lunch in his hand and lowered his hand while standing there. Bookah was patiently waiting and when the hand went down, my dog naturally thought Dick was being kind and offering her his sausage...Natural though, eh, Dick?
)
Alan