Getting older packages from ppa

Yes, you can install a specific version of a package with apt-get install pkg=version but the version you want needs to be available from one of your APT sources.

e.g.

$ apt-cache policy dpkg
dpkg:
  Installed: 1.16.12
  Candidate: 1.16.12
  Version table:
     1.17.1 0
        800 http://localhost:3142/debian/ unstable/main amd64 Packages
 *** 1.16.12 0
        900 http://localhost:3142/debian/ testing/main amd64 Packages
        100 /var/lib/dpkg/status

in this case, both 1.17.1 and 1.16.12 are available to APT. 1.16.12 is installed.

Like the main Ubuntu archive, PPAs remove superseded packages. So, only one version is available for each, Ubuntu release, in a PPA.