The thermal max for Ryzen is 91*C, anything under that is fine, so 70*C is perfectly safe even if it were 24/7. Any shortening of life isn't going to be noticeable, it's not going to do any more damage than regular heat/cool cycling does, you'll replace your system long before the CPU dies, just look at all the people who overclock and use higher than stock voltages on the CPUs for years without issue, myself included.