I am not familiar with pip; after having run the command you suggested to install meson:
$ pip3 install --user meson
Collecting meson
Downloading
https://files.pythonhosted.org/packages/18/ba/0f3d6aef4ba484f59e4d3a00678c4322295976ec1db35c5929a8c1901099/meson-0.51.1.tar.gz (1.5MB)
100% |████████████████████████████████| 1.5MB 674kB/s
Building wheels for collected packages: meson
Running setup.py bdist_wheel for meson ... done
Stored in directory: /home/joachim/.cache/pip/wheels/56/ce/4f/5ed3e8d6a5e2b826d3625bfe32c7205e4c67043817d955cc00
Successfully built meson
Installing collected packages: meson
Successfully installed meson-0.51.1
it does not seem like my system finds meson-0.51.1 anyway, but still finds the old version. What do I need to do to have the newer version of pip run? My guess is that the executable meson-0.51.1 is located at ~/.local/bin/meson - but do I need to to anything more than to point out that executable in a symlink that I create under /usr/bin ?