What's the adjective for someone who isn't loose with their thoughts/opinions/judgements?

In my professional and personal life I've been trying to listen more and talk less. I tend to offer my thoughts/opinions/judgments where they're not needed and I'd like to stop doing that. It's been bugging me to find a name for a person who isn't so loose with their thoughts/opinions/judgements. The name for a person one might say "Oh yeah, David, he's a very ______ kind of person." Someone beyond reproach keeping gossip and such to themselves...

I like "reserved" for this purpose.

reserved

ADJECTIVE

Slow to reveal emotion or opinions.

"he is a reserved, almost taciturn man"

I believe reticent is exactly the word you're looking for. It means you don't talk about your own thoughts and such readily.

From Oxford Living Dictionaries

(adj.) Not revealing one's thoughts or feelings readily.
‘she was extremely reticent about her personal affairs’

I like tight-lipped.

: reluctant to speak; taciturn [Webster's]

She was tight-lipped when asked about her last boyfriend.

Taciturn isn't bad either.

I believe 'judicious' is a good word to describe such a person who doesn't offer unsolicited advise, doesn't pass judgement easily.

Judicious -

using or showing judgment as to action or practical expediency; discreet, prudent, or politic: Example: judicious use of one's money.

having, exercising, or characterized by good or discriminating judgment; wise, sensible, or well-advised: a judicious selection of documents.

Considered is sometimes used with the opposite sense to 'hasty / outspoken':