That’s tricky. I would certainly concur with CFH’s advice; behaving in this way will give you more gravity, whether it gives you gravitas is altogether different.
For me, to truly have gravitas you need an absolute conviction in what you believe and say and not give a f*** what anyone else thinks.
In my workplace (aerospace) we have an senior engineer; highly competent, highly educated. He picks his words with care, speaks slowly and deliberately and if he doesn’t know he’ll say so. Most of all he can be relied upon to state his honest opinion. This will often turn the spotlight onto his management or other departments / individuals (and I don’t mean in a blaming way – just stating facts). Nobody ever interupts him, and everyone has the highest respect for him. He also happens to be extremely (independently of work) wealthy. Personally I believe this gives him a freedom to speak his mind that few enjoy. The irony being that because he doesn’t need the job, he’s very good at it.
I quite like this definition:
‘Gravitas: My notion of gravitas (and I know there are different views) is that it is the external evidence of a deeply held conviction that the individual is totally competent to do what is expected of them and handle anything that comes their way, without feeling the need to prove themselves.’
Few people in today’s workplace are able to live up to that level of integrity.
On a more practical note – I’d ask the feedbacker to be a little more specific