About 10 years ago I was in a similar situation and age like you are, had 95% only worked with Windows servers and clients and had just made my MCSE. I switched my job to a AIX and Linux environment and dropped all that Windows experience at once and did not regret it at all.
I already liked to work typing in commands etc. in my little contact with Unix and Linux, instead of clicking around predefined options in some menues that just change names and places in new versions
, waiting for patches to fix Blue Screens etc., rendering you somehow helpless (way back then).
Additionally to Corona's info, you might have a look at this:
The Linux System Administrator's Guide
and
About Debian Linux
In the second link there are some thingies on the left side which you could use as small projects.
Having a new job where your boss knows that your are somewhat new to the OS, letting you have some time to get familiar with it and some nice coworkers that are willing to show you things would be a good environment to get good skills. Having less of this and much preasure on you can work well to get you good skills, but you'll have a lot more stress and will often have to learn things the hard way.