Newer homes vs old homes- SFH Portfolio

Hi,

Currently I have SFH homes around 8 and all of them are 1990 or 2010 built. The homes are newer but same time cost me more to buy (190-220K ish average). Houston TX. They all have been rented out. . I never bought it to flip or sale and plan to keep it for 10 years. Basically I get $0.98- $1.05 per SF of the house. Properties all paid up.

I want to know from investors who buy old homes 1960-1980s which cost less (assuming 15-20%) discount due to age.  What are your thoughts.  Buying old homes can save money but also rent is less and I am not sure about maintenance cost.

Anybody who has looked into this factor of creating portfolio of newer homes only or old homes and how do they perform?