Does the following sentence seem natural to native English speakers?
"I have been gearing up for a career in XXX since then."
Also, does this sound formal? If not, what do you recommend instead?
Thank you in advance.
The use of 'gearing up' is relatively informal, but more than that it might be more appropriate in areas like 'man' sports, marketing and general business, and less so in more traditional areas, like linguistics.
Try 'preparing' as a neutral replacement.
I have been preparing for a career...
It is always worth checking anything that looks like a phrasal verb in more formal situations.
The phrase "gearing up" usually implies a series of increasingly important/relevant tasks in relation to preparing for something.
e.g. The company has been gearing up to go public by doing x, y, and z.
If you can point to a specific set of actions that you have taken, then yes, you have "geared up". However, it may be more apt to use "preparing for" or "working towards [a career]" instead.
to gear up vocabulary.com
of several senses of gearing up
precondition: put into the required condition beforehand
seems to fit your question the best.
I have been gearing up for a career in X since i was a young adult.