"in a formative stage" is correct and can be used in written English.
You can use it to describe something in the process of being developed or established. For example, "The department is still in a formative stage and will take another three years before it is fully operational."
"Everything's in a formative stage," he said.
"We're still in a formative stage," Marzio told me.
"We did not fail them intentionally, but our community was in a formative stage and our youth searching to fill the vacuum within received wrong advice and training".
As a designer, she thinks of herself as still being in a formative stage, her style sense as fungible as her public persona.
Despite these advances, applying SIP theory to the design of interventions to promote social competence and prevent aggressive behavior remains in a formative stage.
On a parallel track, but still in a formative stage, are efforts to reintegrate lower-level Taliban into Afghan society "We're on the cusp of beginning, of supporting, the Afghan beginning of reintegration," General Petraeus said.
Her affinity for washed-out, goth-tinged leathers and stretched-out shapes is understandable: Ms. Yogev, the designer of Grai, based in Los Angeles, apprenticed with Mr. Owens at a formative stage in her career.
Possibly we heard Brigitte Bardot cooing Un Jour Comme Un Autre at a formative stage in our development, or we had a dream in which Vanessa Paradis was doing suspect things to Joe Le Taxi.
All double-entendres are intentional, as when Janeane Garofalo is remembered as being "on 'Ben Stiller' " at a formative stage in her career.
"Duke provided me with a quality education at a formative stage in my life, and everything I've done since then has been a continuation of those experiences.
One must then consider that prediabetes is a formative stage in the development of CVD, and thus may be more amenable to efforts at CVD prevention, whether by lowering risk factors or glucose itself.
