Use part of what you have for a down payment to the owner ( keep some in reserves for unexpected issues) see if he will carry the remainder of the loan for at least 5 years or possibly the life of the loan depending on his age and what he is needing/ wanting out of the deal.

I replaced three roofs on my properties over the 10 years at significant cost.(2) Do not discount the age of the housing stock. 

Found a place where the numbers were there but just too many problems between sketchy neighbors and the age of the house to pull the trigger.

Be sure to check the unknowns, roof age, hvac, plumbing.

@Solomon Morris greetings,Consider the age of the ductwork itself as well.

No need to get tangled up with someone who will have access to your pocket book and with whom you could potentially produce another living human being that would require time, energy and money.If you do this one step, you'll already be ahead of 50% of my tenants who got preggers/had kids out of wedlock and are now single parents trying to make it on a GED and a $10/hour retail job.P.S. 

So basically, "back of napkin" to see if it loosely works...making an offer, if offer is accepted, during the due diligence, find out the age of everything...re-run the exact numbers and then make adjustments accordingly.  

Do a little market research around the neighborhood to find out rental rates for various properties and how rents differ based on age, condition, parking, neighbors, amenities, view, etc. 

5) is there an age limit for you to be able to rent it out?

In quite a few different ways, but the age and repairs needed were the heavy price movers.