Just an FYI - toe walking is not always a developmental red flag. I was a toe walker as a child because of a physical issue - my achilles tendon was (still is) too short. At your son's age, it didn't cause me too much trouble, but as I grew, it became painful. Nowadays this is addressed surgically (usually around 10 years old, before the growth spurt that comes with adolescence), but when I was a child (I'm 45) it was addressed through physical therapy. It took close to two years to get my heels to consistently touch the ground when I walked, and to this day, if my heels are flat on the floor, I can barely bend my knees. I still do daily stretching exercises to keep my calf muscles and tissues stretched out.
So do pay attention to the toe-walking, but do not assume that you know what it means. A physician can evaluate the child and tell you more.