In just under 12 minutes, I can run 1 mile or 1.6Km. I was 58 years old when I ran my first ever mile on a treadmill. That took me 15 minutes at that time. The best I have ever run a mile is 9 minutes and 56 seconds. I was REALLY pleased that day!
I started out walking and then running for 30 seconds, then walking, then running etc and increased the running sections as I got fitter until I did not need a walking section. After this, at times, if necessary, I slowed the pace to a slow jog, to recover, then increased the pace again. I was advised to set the incline at 1 or 2, to give additional workout, similar to running outside (takes account of going up and down pavement edges / footpaths / uneven ground, so i have always set the incline.
I tend to do different things on the treadmill, if using it a lot. Sometimes, I go by time and in this case, will use the count down or up of the timer to go faster for the last 10 seconds of a minute, increasing that to 20 seconds. Sometimes, I put the incline up and the speed down for a while, reversing that to get running faster. Sometimes I go by distance and try to reduce the time needed to reach a certain distance, such as a mile. Sometimes, I do intervals - set the machine to start me off and warm up, then run as fast as I can for 10 or 20 seconds, then slow down to recover, even to walking pace then repeat. I have done 3 miles in 33 minutes in this way. I do whatever it takes to keep me interested.
I haven't taken my resting heart rate in the past year but it used to be 58, going even lower if i was in the beginners yoga / stretches class at the resting stage.