Can I still get level 60 hellfire ring if I have a level 70 character?
Yes you can. Just acquire the plan from Squirt the Paddler. You'll need some crafting mats, too. But these can be obtained in Adventure Mode by killing the Uber Bosses in New Tristram. To engage the Uber Boss fight, you need the Infernal Machines, which drop from killing the Keywardens.