I have these cracks appearing on the sidewalls of all four of my tires, around the entire circumference of each of them. Does this seem normal? these tires are roughly 4 years old and have 23,500 miles on them. Cooper Evolution Tour 225/65R17
Looks normal to me. Depending upon who you ask, tires will age out in 5-8 years even if you haven't worn them out. Go another year or so, then replace.