Do I have any potential in the academic field? I live in a third-world country. Although I have a second-class degree in IT, I work in the general banking section in a private banking organization. This is possible because, in our country, private banks recruit engineering students (among others) as Management Trainees. They are rotated among various sections in the bank and are trained up for two years. After two years, they are promoted as Executives.

After joining the organization I found that there is huge amount of study involved to get confirmation and to get promotion. Moreover, I don't know Accounting.

Now I am thinking, since I have to study anyway, why not take the GRE and TOEFL, then study apply for a MSc in IT or computer science and then a PhD degree from USA.

I have already been away from academia for almost four years. And, since I am doing a full-time job, I think it will take 2 years more to prepare myself applying for higher education in the USA. At that point I will be 32 years old.

Is a PhD degree from USA enough to find a job at that age?
since I have to study anyway, why not go for GRE+TOEFL, MS in IT or Computer Science and then a PhD degree from USA

Maybe you're aware of this, but "studying" has little to do with getting a Ph.D. It might suffice for an MS, but a good MS involves more than just "studying" as well. 

In other words, if (as stated) your idea is that instead of "study" to get a promotion, you want to study to get an advanced degree, you're in for some disappointment. A graduate degree (especially a Ph.D) involves a lot more "doing" and independent creative thinking.