Spiritual maturity happens over time. That’s why most metaphors for spiritual growth in the Bible are gardening metaphors.
And it follows that some people will mature at different rates than others. Some are self-learners and will seek out resources and read and grow at a much faster pace than someone who is less inclined to do so.
But there are still plenty of people who don’t seem to mature spiritually over time. Their lives look no different than their neighbors’ and coworkers’ lives. They’re not getting more generous. They’re not growing in holiness. They’re not praying or reading their Bible.