He was given real authority in Ephesus while still considered young.
Who Timothy was
Timothy is young, apparently prone to timidity, and given one of the hardest assignments in the early church. Paul's letters to him read like a mentor writing to someone who might quit. The instruction is not to wait until he is older or more confident—it is to set an example now, and to remember where his faith came from without leaving it there.
What men can learn from Timothy
Credibility is built, not waited for
The answer to being underestimated is to set an example in speech, conduct, love, faith, and purity. None of those require seniority.
Inherited faith has to become yours
Paul names Lois and Eunice as the source, then tells Timothy to fan into flame the gift that is his. Received faith is a starting point, not a finished thing.
Timidity is addressed, not indulged
The alternative offered is not bravado. It is power, love, and self-discipline together—which is a more demanding standard than confidence.
Key verses
1 Timothy 4:12
Youth is not the obstacle—the example is the answer to it.
1TI.4.12
12 Don’t let anyone look down on you because you are young, but set an example for the believers in speech, in conduct, in love, in faith and in purity.
An inherited faith named, then handed back to him as his own responsibility.
2TI.1.5-7
5 I am reminded of your sincere faith, which first lived in your grandmother Lois and in your mother Eunice and, I am persuaded, now lives in you also.
Appeal for Loyalty to Paul and the Gospel
6 For this reason I remind you to fan into flame the gift of God, which is in you through the laying on of my hands. 7 For the Spirit God gave us does not make us timid, but gives us power, love and self-discipline.
That youth is not a reason to wait. Paul told him to set an example in speech, conduct, love, faith, and purity rather than deferring until he was older. He also addressed Timothy's timidity directly, offering power, love, and self-discipline as the alternative.
How old was Timothy?
Scripture does not give an age. He was young enough that Paul thought it worth telling the Ephesian church not to look down on him for it, and he had known the Scriptures from infancy through his mother and grandmother.