I started flipping when I was your age.

What sort of numbers should I be using for maintenance and cap ex so that I make sure the investment stays profitable as it ages?

Rent will be lower than taxes, mortgage, insurance, maintenance and he is near retirement age. 

Old houses have cast iron pipers that will disintegrate (because of age and/or foundation shift).

In addition to this if distribution is taken prior to normal retirement age - you would have to pay penalties.

@Nathan RealphBy the date of the property as follows a class a building his new construction a class B building is 10 to 15 years old well-maintained with a little deferred maintenance class C building built within 30 years Shows age some deferred maintenance class D building over 30 years old no amenities low occupancy needs work

The rehab will start to age.

Due to his age, he is not interested in seller financing (due to the 15 year term) He is happy to help me in any way, and I plan on asking him to do a lease option on a couple houses.If I can structure it to where I net $100-200 a month, and have the option to buy in 1-3 years, that would be great for me.

As said before, the property is 100 years old, and certificates of occupancy are never used on properties of that age so I'm confused as to why now it's what they are using to contest the occupancy?

@Randy HamricMight not be the answer you're looking for, but personally if I had $135k to put into real estate at your age, I wouldn't quit my job right away.