My girls didn't walk until about 14 months. They pulled themselves up and walked along things for a good 3 months before they were finally brave enough to walk on their own. They were scared to walk by themselves and were very skeptical when starting out. Its totally normal for babies to not be walking yet.

He is not delayed. Babies walk at different stages. Some start walking between 14 and 16 months, perfectly normal children. Research done has proven that baby walkers do not necessarily help children to walk faster but may actually slow them. I would use the push walker lesser and encourage him to reach for things more on his own. Definitely nothing to worry about at that age, as long as his physical anatomy is right (e.g normal legs, feet flat on floor while standing e.t.c)