God is limitless and is not confined in time and space. He is a Spirit (John 4:24) and no one has ever seen Him (John 1:18). We are created by His own image (Genesis 1:27). His image is the Spirit and not what we look like physically. This then means even though we are confined in the space of our physical bodies, our "spirit" is limitless and its confinements are determined by our soul (mind). What we achieve is even more than we can think and imagine because of the power within us (Ephesians 3:20) because we are more than just our bodies can do, since our flesh is limited. He knows what we are capable of in Him when we abide and trust in Him, the impossibilities become possible as the spirit is not led nor driven by physical laws.
David killed Goliath at the age of 17 years, yes the accuracy of his slingshot (with much practice protecting his sheep from wild animals) ended the physical life of the giant but the might of the sling was from the unseen power of God in David (1 Samuel 17). What was seen as an impossible situation for David (a small boy fighting a giant) was possible through God's power that was within him. This story is an example of how the spiritual and the physical converge. Age is not a factor of what God can do through you, I believe it's through availability, will and total surrender to Him. Spiritual maturity through worship, prayer and studying from the scripture not only brings one closer to God but an individual is re-introduced to oneself and who one was created to be by the One who made him/her. A spirit is eternal and exists forever, and where we go after the earth is determined by our choices.
I have heard people say that things are birthed first in the spiritual realm before the physical realm. Since the spiritual realm is unseen, to pray for things into being (according to God's will) takes Faith which is to hope for things not seen and believe that they are hence being thankful to God for receiving what one just prayed for before it is present. Just like the body needs food, feed your spiritual man by the meditating upon the word which will direct your path (Psalm 119:105) into your destiny that God had already planned. Limit not the power of God within you.