Compile with gcc on Macos 10.14.5 that will support earlier versions of Mac

I have a c ++ code that I wrote that uses almost nothing, which is not the language itself (except using osascript).

After compiling it on my operating system version (10.14.5) with the following flags: D_DEBUG, Os, Wall, Wextra

I found that it was not running on older operating systems (in 10.13 for example - it raises an error that it can only run on 10.14 or later)

What are the right flags to use to tell GCC, that I want to support as many MacOs versions as possible?