Katbot, if it works for you, have at it!
Having a gym partner is a huge help, I've found... it's great that you go with your dad!
My parents are slowly getting back into exercise, which is wonderful. My dad is 71 and my mom 66, and while he has an active past, my mom sure doesn't. But she just bought a bike and while she's scared of riding since her last time was more than 50 years ago, she really wants to do it. She's always mocked exercise as something jocks do, but now that she's seeing signs of decline in her balance, she's seen the light
I love swimming... and climbing walls can be intense! Stairclimbers are beasts. Personally, I find them too hard for me at my current weight... respect to you! You are going to be jacked in 19 months!
Finding something you love I think will make time blow by, and while you will get tired, you will also be exhilarated. Like yesterday, I went for my first bike ride in 10 years. I rode 1.5 hours. There is no friggin' way I would have ever done 1.5 hours on a treadmill