Ansible has a version_compare
filter since 1.6.
You can do something like below in when
conditional:
when: ansible_distribution_version | version_compare('12.04', '>=')
This will give you support for major & minor versions comparisons and you can compare versions using operators like:
<, lt, <=, le, >, gt, >=, ge, ==, =, eq, !=, <>, ne
You can find more information about this here: Ansible - Version comparison filters
Otherwise if you have really simple case you can use what @ProfHase85 suggested