I don't know if you would be able to buy now even with a HUGE downpayment. Credit heals rather quickly but in all honesty, you are not in a position to buy. Work on serious credit repair, pay off credit cards and save a down payment. You will thank yourself in the future. There is nothing wrong with renting until the time is right.
First and foremost would be does he have the ability to repay the loan? What is his source of income? Age does not really play into it as much as the ability to repay the loan.
I agree with John. I would highly recommend meeting with several buyers agents and find one that will take the time to set an appointment with you, sit down and explain the entire process and then ask them for a mortgage recommendation. If you call agents and the first thing they want to do is show you houses, they are more concerned about the sale than you. A great test is to call agents and simply ask to go look at a house. Everyone that tries to show you that house, is not interested in making sure you are taken care of. Go with the one that wants an appointment first (in office, coffee shop, restaurant, etc) and is willing to take an hour to explain the entire home buying process. That is when an agent is doing what we are hired to do and serving you. Anyone can open doors, a qualified buyers agent REPRESENTS you. They will also have a mortgage professional that they trust and they will be more than happy to make the recommendation.
Like Andy said, the answer is in your contract. The fact that there were 4-5 extensions needs to be a warning that this buyer or this bank is not in the position to make this deal happen.
The end needs to be the end. The government needs to let the market settle and quit artificially inflating it.