will age and lack of experience make it impossible to change my subject of study?

I'm 33 years old and I have my master's in physics from a relatively good university in my country.

I have 6 years working experience as a foreign commercial executive which I hated every minute of it, but I needed to make some money. I have to add that I have visited different factories in different countries during the missions I went.

About two years ago, I resigned and diligently went for learning everything about electronics and microelectronics which were always my desire. Now, I feel quite confident in embedded systems programming and everyday I study so hard whatever related to digital electronics but I have not yet applied for a job in this field.

I know this is what I always wanted. I have average grades in university and good GRE.

What are my chances to get admission for PhD in electronic engineering in one of US universities?