I actually had some grad students beg to rent one of my houses but since they didn't meet the criteria, I told them their parents would have to co-sign and demonstrate all the same criteria and their parents were not willing to do that. 

@Brent Langlois  all title companies are different.there are a few in PA were I was selling some prop.. and they would not accept wire instructions unless I was physically in there office dictating them  in person.I said well that's kind of tough being I am in Orygun... so they fed ex a check.I don't like checks from small non national companies there was a title co. in Texas that went busto and many folks lost tons of their proceeds as the money went missing and company closed its doors.. so I 99% of the time want my funds wired. 

And at least hear in the Denver metro area, I know that while many of the areas immediately outside of Denver have not yet passed any laws, they are all considering it and are looking strongly at the primary-residence-only model.

My house in Colorado wasn't comparable to others in the neighborhood.

I gave my $300,000 move-in ready beautiful vacant home to this large well known local co in Oct 2016.( Ive owned and self-managed another very similar rental in the same subdivision-- since 1998--and it has never had one day of vacancy in 16 years-- rented at $1860.)This professional pm co put all utilities in their name on my new property and turned the hot water heater ON and the Water ON ( even tho the main water cutoff valve is easily accessible in the coat closet beside the garage, the entire 3 months they 'managed it').They let the property sit VACANT OCT-NOVand on their "routine inspection on Dec 1, to make sure hobos had not moved in" they SAW the water heater in the garage was spewing (at full blast) A 20' stream/ fountain of HOT WATERand that the entire finished closed garage was covered COVERED !!

In Colorado the only people that aren't issued at least 1 dog are the "cat ladies", so you cut your renter pool by about 75% if you do not allow a pet.

If the CO wasn't never changed, then it is an illegal 2 family.You can protect yourself by verifying which is which and staying away from an illegal residence unless you want to go through the trouble of getting the CO updated.

I am a licensed HOA manager in Colorado.

With regards to co-mingling, if you pay an expense from your personal account, then have your LLC reimburse that expense, does that help protect the integrity of that entity in the case of a lawsuit, etc?

And if he is I would require the parent to co-sign and be financially responsible.