I am looking to get a 2009 F250 with 139,000 miles on it is it a good buy?

i am 21 and it will be my first vehicle and i don't know too much about diesels. It is a 2009 Ford Super Duty F-250 Lariat Power Stroke Diesel 4X4 with 139,000 miles for $30,000. What would be the average MPG, what is the break-in mileage, what is the average mileage and what is high mileage? A lot of questions i know but like i said i don't know anything about diesels and i just want to make sure it is a good buy.

Read more: I am looking to get a 2009 F250 with 139,000 miles on it is it a good buy?