Software Engineering is an interesting mix of practice and theory. On the theory side, you should make a habit of browsing / googling for things that are a good intersection of interesting to you and novel. Be forewarned, some of the common places to get information (like stackOverflow) can be very intimidating.
The standard expiration date for most checks is 180 days (six months) and personal checks are included in this policy. In the United States, banks are privately owned and not government operated so banks do have the right to refuse your deposit if there happens to be any suspicion of the item's negotiability.
Yes-they do expire and the period remains 18 months. When you login, your mileage balance appears in a box on the right hand side of the screen. Hover over the words mileage balance (underlined) and the expiry policy appears.