“mature” and “emotionally cold” are two different things.
People who are emotional indifferent may seem “mature” at first glance, but as you become closer, your frustration will grow as they will be unable to respond to your emotional needs.
The same thing applies to emotional sensitivity and volatility. Emotionally sensitive ones can be tolerated, but volatility is a deep-rooted issue and not curable without therapy. Over time they will claim too much of you, will not contribute as much in the relationship and make you feel exhausted.
My favorite dating advice is to give people time. Spend enough time with them before you make a decision, people can be tricky to understand because they are complex creatures.
(Part of a conversation)