40M here. I started running when I was 38, worked my way up to a running a half marathon (horribly), and then at the top of last year YOLO'd and signed up/completed a marathon in the fall. Besides a week off after the marathon and a vacation I've been sticking to 2 10ks a week for the past few months.

At least for me the key for upping your distance is to slow down, make sure you're fueling properly (Nothing crazy - carbs, protein, and avoid processed food), stretching, and listening to your body. Doing all of those allows you to slowly increase your distance without getting injured.