The thirtieth year seems to be a very significant time in people's lives - both in the Old and New Testaments.
Joseph was 30 when he became ruler in Egypt. By the time Joseph was 17, God had already revealed to Joseph in dreams that he had a purpose for his life. It is wonderful when a young man is so sensitive to God that at an age when most teenagers have filthy dreams, he has dreams from God. Look at the things Joseph suffered - jealousy from his brothers, false accusation from an evil woman, and jail. In those days jails were terrible dungeons with rats, worms and cockroaches crawling all over the place. But it says in Genesis 39:21 that "the Lord was with Joseph".
David was 30 when he became king. In 1 Samuel 16, when Samuel told Jesse to call all his sons for a sacrifice, Jesse called only the first seven. He did not even bother to call David, the youngest - obviously because nobody thought much of David. He was the baby of the family - perhaps 15 years old. When young David was called, he did not even know what was happening. But God had been watching him and had seen his devotion and love for the Lord. As soon as he came, the Lord told Samuel "This is the one" and Samuel anointed him and the spirit of the Lord came mightily upon that young teenage boy.
Jeremiah was a young man when God called him to prophesy. God said to Jeremiah "Before I formed you in the womb I knew you. Before you were born I consecrated you and appointed you a prophet to the nations." (Jeremiah.1:5,6). God had His eye on us even when we were just microscopic specks just conceived in our mother's wombs. He has a plan for our lives just as He had a plan for Jeremiah. This is a great encouragement for all who are young. The Lord told Jeremiah "Don't say I am a youth, because everywhere I send you, you shall go and all that I command you, you shall speak" (Jeremiah 1:7). And then the Lord spoke a word to him that He often spoke to His prophets: "Don't be afraid, because I am with you to deliver you" (Jeremiah 1:8).
Ezekiel was 30 when he began his ministry. Ezekiel was the son of a priest who was training to be a priest (Ezekiel 1:3). But when he was 30 years old, God suddenly called him to be a prophet (Ezekiel 1:1). Ezekiel must have submitted to Jeremiah, in his younger days. He must have listened to Jeremiah's prophecies and studied them as a youth. God Who saw the faithfulness of this young man, decided that Ezekiel would be a prophet and not a priest. One day God opened the heavens over Ezekiel and gave him visions of Himself and a message for His people.
Daniel never knew, when he started out being faithful as a young uncompromising man, what a tremendous ministry he was going to have. He just remained faithful to God in little things and big, and God accomplished a great ministry through him. He was probably around 17 years old when the book of Daniel begins, and about 90 years old by the time the book ends. He lived through the entire 70 years of captivity, and he was faithful all the way through. That was why God could use him to begin this movement from Babylon to Jerusalem. Even today, God can choose a 17-year-old youth and make him a prophet and empower him to take a stand for Him.
Zechariah was a young man who prophesied along with Haggai. Although Zechariah was younger than Haggai, God gave him much more to prophesy. God is no respecter of age. He began to give Zechariah visions and prophetic messages when he was very young (Zechariah 2:4). God can pick you up when you are young, anoint you with His Holy Spirit, team you up with an older, godly brother like Haggai and finally give you a wider ministry even than him. Zechariah had a blessed ministry of encouraging discouraged people.
Jesus was 30 when He began His earthly ministry. Even Jesus needed that training to submit to Joseph and Mary for 30 years before He entered into His ministry. How much more we?
Most of the apostles were around 30 when they began their ministry. Even today, it is probably around that age that God wants to begin to lead His children into the specific ministry that He has for them. But prior to that date, God has to spend many years in preparing us for that specific ministry. If you surrender to God totally and allow Him to prepare you during your teens and twenties, then you can be ready by the time you are 30 (or 35), for that specific ministry that God has planned for you.