Yeah agreed - it's not such a bad thing! My daughter, who's my 2nd baby, I found STANDING on the dining room table one day when she was 17 months old. Little monkey. She's always been agile - sat up at 5 months, crawled at 7, walked at 11 months...but my son was way later on his gross motor development. At 17 months he still wasn't climbing either...and couldn't jump with 2 feet off the ground until well after 2. She's been jumping since about 20 months (she turns 2 next week). Anyway, point is, they're all different. My pediatrician has developmental checklists for each age - they actually have them posted on their website which is great for when I need to check something in terms of what they should be doing.
I'd be more concerned about his gait when he's walking, whether he seems unsteady at all or you notice anything unusual..otherwise he's probably just developing a little later in terms of climbing. As always, just put a call into your ped to ask what they think. But I bet in a couple of months you won't believe you posted this as you're rescuing him from climbing on the box he just put on top of the couch!