Key I was 17 when I was saved, I'm 59 now, Jesus has been faithful all my life and his love towards me has never gotten cold.
I'm going to make a couple of assumptions here so if I'm wrong please correct me. I suppose you are a male and if you joined this kind of group you are probably serious.
A few things.
1. Seek out a strong men's bible study, find one that is Christ-centered, values scripture highly and the men themselves are seeking Jesus as you are. If not, find some place else, if you need to go outside your own Church do so.
2. Find a good mentor, someone who loves Jesus and will take the time to invest in you. Learn how to live out your faith from godly older men their counsel and wisdom will be of great help to you.
3. Stay away from lukewarm, biblically illiterate people, refuse idle chatter, or those who name Christ but find their real pleasure in gaming, sports, girls, partying etc. The very thing you need to mature you...they do not have.
4. Invest your time in learning the word of God, study, pray, compare scripture with scripture. Become a good student of scripture, learn to take delight in God's word, his wisdom and from that word he will begin to reveal himself to you.
5. Invest your time in prayer, learn to spend hours in prayer, how? It starts by giving God 5 minutes, then 10, then 30 and so on. Do not rush yourself and do not go from prayer to idle chatter or immature boyish talk with your friends. If you do, you will find it draws you away from spiritual realities into the bustle and hustle of worldly thinking again.
6. Be filled with the Spirit of God, seek God to empower you for his work, speaking, sharing your faith. Be a doer of the word. Do not learn then be silent, do not seek compassion for others and not go out and express it.
7. Refuse all cowardice, timidity, shyness be bold in your faith, allow no one old or young to intimidate you so as to quench the Spirit of God within you.
You have one great commission and that is to make disciples while you are being disciple-d. The commission of Jesus is your commission and its my commission as well.
Weakness, hypocrisy, cowardice, lack of confidence all find their strength in learning the bible and not practicing what you read. Including... hearing sermons and not applying them immediately to your own self. Feeling compassion and mercies and shutting up those godly impulses over some fear or some perceived inadequacy.
A new Christian can be greatly helped by older wiser men who are zealous for God's word and their own holiness. Find one, pray the Lord Jesus provides you one.
Let us know specifics if you are willing.