"sufficiently mature" is correct and usable in written English.
You can use it to describe someone or something that is old or developed enough to do certain tasks or behave in a certain way. For example, "The students in this class are sufficiently mature to handle the topic of cyberbullying."
Many of the actors are not sufficiently mature or experienced.
In fact, it is a novel that she didn't expect to tackle until she felt sufficiently mature.
Focus in the later stages of a race can sometimes come at the cost of keenness in the early part when a horse is fitted with cheekpieces, but Henderson is satisfied that Long Run is now sufficiently mature to cope.
Our understanding of disease biology and treatment paradigms in diffuse large B-cell lymphoma (DLBCL) is now sufficiently mature that we are poised to enter a new phase of hematological oncology.
However, there are two main barriers to this: doubts about whether fire safety engineering is yet sufficiently mature as a profession; and concerns about whether the probabilistic nature of fire risks make fire safety engineering unsuitable for self-regulation.
Although eager to work on The Primevals, Allen said he was not yet "sufficiently mature professionally" to undertake a project of that size, and he felt Laserblast was "something that was more manageable".
This happens when one of the screenplays is either nearly done or seems sufficiently mature".
The eggs hatch and start to grow, and when their jaws are sufficiently mature, they commence feeding on one another.
This, in the case of the Negro, the American republic has never become sufficiently mature to do.
Claire is enthusiastic but not sufficiently mature as a businessperson; she could play a more suitable role, such as strategist.
The young fish are bred in the controlled environment and when sufficiently mature are released into the open sea.
