I wouldn't worry as much about the age as I would what it would cost, how much it would rent for, how well it is built and when major repairs will be needed (ie how long will the roof last).Also for the two-are they both condos (ie strata/condo fees) or is one freehold and the other a condo (ie one has condo fees and the other doesn't)? 

If have RCv vs ACV all that means is a 90%+ discounted roof replacement every 17yrs on average.

Multiple improvements done on this duplex in 2021, including new roof, gutters, flooring, drywall, electrical, appliances, and heating/cooling unit for the second floor.

Structural, roof, mechanicals, cosmetic? 

Roof and HVAC are in good condition.

It recently had some roof and ceiling damage and we are looking to sell.  

However, given a lax board and the community's preference to avoid assessments and projects I believe no major repair or replacement work has been done since the building was built in the mid 80's (i.e. roof, plumbing etc.,).

We hired Bildwise for a renovation of our 1965 single-family home that included complete electrical rewiring and updating, roof replacement, light kitchen and bathroom remodeling, new flooring, new interior paint, and masonry repair.

I had never been to any auctions and never bought any real estate, yet prevailed at the auction, buying a 17 year old brick 3 bedroom house with hardwood floors, ceramic baths, and a brand new roof. 

Additional details: You would never know there was a single wide originally - the house is now 75% new/stickbuilt and all roof/siding is seamless between the OG trailer and “addition”.