But won't that reduce its life?? And how can I fix it
Technically speaking any amount of heat reduces a CPU's life span. But the temperatures you're running it at aren't going to damage it or reduce its life span in any significant capacity and those temperatures are about what everyone else gets with that processor give or take a bit.
The stuff I described with sporadic temperatures and high voltage also shouldn't hurt your processor either. I'd be
very surprised if your CPU doesn't make it past the 10 year mark or beyond so you shouldn't have to worry about it dying on you.
And if it does die on you, it will very likely only be LONG after its completely obsolete. I'm talking in the 10+ year range. At that point in time you could probably pick up a new 3600 for like ~$30
But if you're still worried ( I don't feel like you should be) the only real way to get better temperatures is to get a even better cooler but I'd say your current one is doing a good job considering its only ~70c under load.
Some people have tried lowering their voltage slightly which gave them slightly better temperatures but that can come at the cost of performance so I wouldn't recommend it.
If your case has more spots for case fans that could possibly help out a little too. Keeping your computer clean of dust by blowing it out with some compressed air every 2 or 3 months could also help.
But as I said I think your temperatures are perfectly safe, really.