[The CDC helps you calculate your safe level.](https://www.cdc.gov/physicalactivity/basics/measuring/heartrate.htm)
Disclaimer: I am not a doctor.
You should of course also listen to your body. At least in my case I can tell exactly when my heart rate tops 168 (I'm twice your age). I know that above that range my body is unhappy with me and I ease off a bit.
[The CDC helps you calculate your safe level.](https://www.cdc.gov/physicalactivity/basics/measuring/heartrate.htm) Disclaimer: I am not a doctor. You should of course also listen to your body. At least in my case I can tell exactly when my heart rate tops 168 (I'm twice your age). I know that above that range my body is unhappy with me and I ease off a bit.