Octave user under 30 here.
I picked up a Matlab project recently (pattern recognition, electrical engineering etc. heavily use it in my university).
Because I wanted to run it on Amazon and didn't want to deal with all the licensing issues I ported it to Octave instead.
Works like a charm (using it in https://camfinger.com ) and it's actually free like any normal interpreter would be.
Personally I'm more used to other languages and would also tend to python, however I must admit Matlab/Octave is a pretty good way to develop matrix heavy stuff thanks to an extremely good REPL/debugger. That being said, Octave feels pretty slow for loops (lack of a proper jit), so I wouldn't know if I'd really use Octave over Matlab if it were not for licensing issues either. Then again I can rent a lot of cloud time for a Matlab license...