Hey there Dougiemac. I'm 36 years old, 295 pounds and familiar with what you are describing. I'll share my $0.02 on the subject.
I'm not one of those college-educated doctors, but my internet diagnosis is that you are over-weight and out-of-shape. Your back is not strong enough for what you are asking it to do. This can be remedied.
I think it is. My back was sore all the time when all I did was sit at a desk and eat cheese.
I've managed to get somewhat strong on both the squat and deadlift in the last 2.5 years. This coincided with the disappearance of back pain of any type. I still work a desk job but I make sure to spend more time on my feet. I take any excuse I can to get up an move at work.
Before I found barbells I did a lot of back extensions. Those helped too. Deadlifts helped more. Start light and progress sensibly.
Generally-speaking, you'll want to avoid anything that fucks you up beyond expected muscle soreness. But being fat and out-of-shape is not reason in and of itself to avoid anything in particular. That said, be mindful of your joints. Work hard. Get stronger. Drop fat. Become a lighter person. These will all be beneficial to you.
No matter what, don't puss out and use this as an excuse to stop working. Stay at it and don't quit.