Refactor get_age in util/dt

[Danielhiversen]

Description:
Refactor of util/dt.py

Checklist:
If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[robbiet480]

👍 👍 👍 👍 👍 👍 @Danielhiversen. Gonna merge this because tests passed. Coveralls sometimes has issues like the one above where coverage increased but it failed still.

I am gonna loop @balloob in though, because Coveralls is showing the same file (remote.py) decreased coverage, which is an issue I had a few days ago that he had to fix because of bad code he pushed.

[balloob]

It's all good except that you forgot the dolphin of approval! Coveralls should only report an error status when coverage decreased 0.5+%. Not sure what is going on there.