Hey there,
yes, squats will help! Carefully adding weight even more so, as soon as you are sure your squats are pretty enough (safe).
Then: stairs. After I slowly added up to 20kilos to my squats I could control my descend on stairs a lot better.
I am 31 and run stairs as part of my every week work outs since November 2017. Before running stairs I warm up and actually started out with just walking them until I felt comfortable in control.
I have walked the Fisterra Camino for the third time in April 2018. There is a steep descent that stretches a long way before a certain town that had killed me the years before. This time I took it in my stride and pushed on. So that was effort well spent.
Also: Magnesium Supplements! No more cramps since I take these pills
Also: Electrolytes! All that water won't help without these.