Yes, we can grow in spiritual maturity.
2 Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord, (2 Peter 1:1-4)
There are a few things we need understand when it comes to growth.
Just going to share some verses for ya'll to meditate on.
#1 Spiritual maturity is NOT automatic
13 For everyone who partakes only of milk is unskilled in the word of righteousness, for he is a babe. 14 But solid food belongs to those who are of full age, that is, those who by reason of [d]use have their senses exercised to discern both good and evil. (Hebrews 5:13-14)
2 Therefore, laying aside all malice, all deceit, hypocrisy, envy, and all evil speaking, 2 as newborn babes, desire the pure milk of the word, that you may grow [a]thereby, 3 if indeed you have tasted that the Lord is gracious. ( 1 Peter 2:2-3)
3 And I, brethren, could not speak to you as to spiritual people but as to carnal, as to babes in Christ. 2 I fed you with milk and not with solid food; for until now you were not able to receive it, and even now you are still not able; 3 for you are still carnal. For where there are envy, strife, and divisions among you, are you not carnal and behaving like mere men? 4 For when one says, “I am of Paul,” and another, “I am of Apollos,” are you not carnal? (1 Corinthians 3:1-4)
#2 Spiritual maturity is a process
14 But solid food belongs to those who are of full age, that is, those who by reason of use have their senses exercised to discern both good and evil. (Hebrews 5:14)
6 Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation of repentance from dead works and of faith toward God, 2 of the doctrine of baptisms, of laying on of hands, of resurrection of the dead, and of eternal judgment. 3 And this we will do if God permits. (Hebrews 6:1-2)
17 You therefore, beloved, since you know this beforehand, beware lest you also fall from your own steadfastness, being led away with the error of the wicked; 18 but grow in the grace and knowledge of our Lord and Savior Jesus Christ. ( 1 Peter 3:17-18)
#3 To Grow, it takes discipline
2 Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord, 3 as His divine power has given to us all things that pertain to life and godliness, through the knowledge of Him who called us by glory and virtue, 4 by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world through lust. (2 Peter 1:1-4)
12 Not that I have already attained, or am already perfected; but I press on, that I may lay hold of that for which Christ Jesus has also laid hold of me. 13 Brethren, I do not count myself to have apprehended; but one thing I do, forgetting those things which are behind and reaching forward to those things which are ahead, 14 I press toward the goal for the prize of the upward call of God in Christ Jesus. (Philippians 3:12-14)
Meditate on all these points & scriptures... then watch the Lord grow in you!