Your body is an amazing machine. It will achieve what ever you require and expect out of it. You must treat it with care. Feed it, rest it, stretch it.
You can build your endurance it takes weeks and months of training. I use a,”three-fer” method for my build. I start with a certain amount of time and build for three days. On day four I cut way back and give my body a shake up. It allows it to heal and gets it ready for the next challenge.
I also do this weekly. It works the best for me and I have seen good results. I also go by perceived exertion as apposed to heart rate.
I have been at this for years so this works best for me. Find out what your body responds to and then challenge it. It will be an eye opener and a great gift for yourself.
Keep your heart strong! Everything else will follow it’s lead!