My son was the same way. He is now 9 years old and still walks on his toes mostly. I too am a tippy-toe walker and we just assumed he learned it from me. My other son who is nearly 3 does not walk on his tippy-toes and my 9 month old baby doesn't seem to yet. Needless to say, my 9 year old/tippy-toer has very strong leg muscles.
So, have no fear, it shouldn't cause any problems!
It is not the norm, but it is also not unusual. Be sure to have his pediatrician check his muscles and tendons, and if the doctor notes an problem he/she might have a pediatric orthopedist examine your son. It's best to check, but likely things are fine.