In the Hebrew, zichnekhem, "your old men," is derived from zachan, "beard," and meant mature men with a full beard. The emphasis is on maturity and experience rather than on age. These were men who were wise, able to judge what was right and wrong, but they would need to have God’s Spirit poured out on them to dream God-sent dreams that would bless His people.
The Hebrew word, bachurechem, "your young men," is derived from bachar, "to choose, to select." These weren’t ordinary boys. The Hebrew has another word, na‘ar, for that. These young men were fully grown, about 20 years old, full of vigor, and unmarried. Proverbs 20:29 refers to their koach, "strength, stamina." But even they can weakly totter and fall in the race of life (Isaiah 40:30). They need the fullness of the Holy Spirit if they are to see God-given visions and be used by the Spirit to carry them out.
Some have supposed that the visions of young men look to the future while dreams of mature men look back to the past. This is not biblical. The whole Bible has a forward look. The word "dream" (Hebrew, chalom) is mentioned over 60 times in the Old Testament. Sometimes it refers to ordinary dreams (Isaiah 29:8; Psalm 73:20), but it often refers to prophetic dreams or dreams that give a revelation of God and His plan or purpose. Jacob’s dream of the great, wide ladder stretching from earth to heaven (Genesis 28:12–15) and Solomon’s dream at Gibeon (1 Kings 3:5–15) are examples. God used these and many other dreams as an indirect means of communicating with His people. Moses was the only one in the Old Testament that God communicated with directly (Numbers 12:6–8). The corresponding Greek words in Acts, enupniois enupniasthesontai, "dreams they shall dream," could also be translated "they shall have visions in dreams." This again indicates dreams and visions being used somewhat interchangeably in the Bible.