Getting off on just probation for aggravated robbery is very unlikely even if the aggravated robbery was the persons first criminal offense and they have no other criminal record.
Aggravated Robber is classed as a felony and when you're charged with a felony and aggravated robbery you're likely to face up to 15 to 25 years minimum in prison or even a life sentence depending on the state and their laws.
If the person is charged with aggravated robbery that means the person who robbed the place was armed with a deadly weapon and threatened the persons or peoples life with the deadly weapon and that makes the offense more serious than just a theft.
If the person were unarmed then they would be charged with robbery which might get them off on just probation but very unlikely as well and even then you're likely to face at least 15 years in prison just for robbery.