From what I have heard it was three times.

First time at age 17
Second time at age 21
Third time at age 32

The second time is the least undisputed since there are a lot of evidence for it.

This guy however claims he was convicted at the age of 17
http://splashurl.com/k435bjc

According to Joseph Smith wikipedia page he was conviter of banking fraud in 1837
http://splashurl.com/l8sszw3

This time he didn't get arrested because he fled to Missouri.

Does anyone has an idea how much of this is true.

One of the supposed convictions for fraud was really a preliminary hearing for disorderly conduct in New York, so that one is greatly exaggerated. In Ohio, the Kirtland Safety Society or "bank" wasn't properly chartered, which was fertile ground for civil suits and criminal charges. I'm guessing that Smith was probably convicted in absentia after he fled Ohio following the general banking panic of 1837. I'd like to learn more about that.

In the Nauvoo period until his murder, Smith had to evade various creditors trying to execute civil judgments against him. That's why, as William Law noted, all the properties were put in Emma's name. I'm sure that many of those judgments came from Ohio, although some of them arose from debts incurred at Nauvoo.

The biggest source of arrest warrants was Missouri, and the charges were usually for violent crimes or treason. I'm not aware of much financial activity by Smith in Missouri.

Smith was convicted of fraud in 1826, when he was 20-21 years old.

However, the First Vision supposedly occurred in 1820.

So, what this means is that Mormonism was founded by a convicted fraudster. Isn't that appropriate!

Also, Smith was committing fraud during the time period when he was trying to prove himself worthy to receive the gold plates.

This is one area that isn't as well documented or accessible as other facts about the early church.

On the first court appearances, he was just told to get out of town and never return rather than convicted.