I wrote https://github.com/toddjm/projects/blob/master/science/dqmc.f https://github.com/toddjm/projects/blob/master/science/dqmc.... in 1999, and it compiles a

I wrote https://github.com/toddjm/projects/blob/master/science/dqmc.f https://github.com/toddjm/projects/blob/master/science/dqmc.... in 1999, and it compiles and runs just fine with gfortran on my Mac. So I'd say you're good for at least 23 years :)