I just installed Linux Mint on a new computer, and when I want to install software with apt-get, it always gets obsolete versions. For instance it installs OCaml 4.01.0 (latest is 4.02.3) and Opam 1.1.1.1 (latest is 1.2)
It is the same in Synaptic.
How can I install the latest versions ? If possible without doing manually, as I'm not at ease with Linux and would prefer the automatic option for now.
By default, the packages which you install using apt-get are the latest stable versions which are selected by the distribution developer team.
It's simple: The package file with specified version is placed on the selected repository. If you want to install the latest version, If other repository provided you can add it to your repo list.. As you also mentioned in your own answer.
Just found the answer. For these packages you have to first do:
add-apt-repository ppa:avsm/ppa