We do not know the actual height of Adam from the Bible, but what we do understand from the Spirit of prophecy is that "Adam's height was much greater than that of men who now inhabit the earth". Adam was of "lofty height and majestic form" and was "of lofty height and perfect symmetry". We also understand that "those who lived before the flood, come forth with their giant-like stature, more than twice as tall as men now living upon the earth, and well proportioned. The generations after the flood were less in stature.".

There are many proofs of giant men. The Bible does not state the heights of pre-flood inhabitants, but we do have valid records of those "giants" of men that have existed in various ages of history.
Height is like any other genetic trait found in humanity. A male and female of lofty stature are more likely to produce offspring with this characteristic than a dwarf couple.
The bible does reveal in the following scripture verses that there were "giants" before and after the flood:
Genesis 6:4-7; Numbers 13:32-33; Deuteronomy 2:9-11; Deuteronomy 2:17-24; Deuteronomy 3:11-13; Joshua 12:4-6; Joshua 13:12; Joshua 17:15; Joshua 18:16; 1Samuel 17:3-7; 2Samuel 21:16-22; 1Chronicles 20:4-8;
What the Spirit of Prophecy reveals in the following passages does confirm the Bible.
Noah's Time and Ours:
Many flatter themselves that in this enlightened age men are superior in knowledge and talent to those who lived before the flood; but those who think this do not rightly estimate the physical and mental strength of that long-lived race. In those ages growth was slow and firm. Men did not, as in the present time flash into maturity early, and exhaust their vital forces. Their minds were of a high order, and were strong and clear. Had these men with their rare powers to conceive and execute, devoted themselves to the service of God, they would have made their Creator's name a praise in the Earth, and would have answered the purpose for which He gave them being. But they failed to do this. "All flesh had corrupted his way on the Earth." There were many giants, men of great stature and strength, renowned for wisdom, skillful in devising the most cunning and wonderful work; but in proportion to their skill and mental ability was their great guilt because of unbridled iniquity. [Bible Echo 07-01-1887]
After the Flood:
The generations after the flood were less in stature. There was a continual decrease through successive generations, down to the last that lived on the earth. The contrast between the first wicked men that lived on the earth, and those of the last generation, was ver great. The first were of lofty height and well proportioned. The last came up as they went down, a dwarfed, feeble, deformed race. A mighty host of kings, warriors, statesmen and nobles, down to the most degraded,came up together on the desolate earth. [Page 83, Early Editions, Spiritual Gifts, Volume 3 1864]
The Conquest of Bashan:
Filled with hope and courage, the army of Israel eagerly pressed forward, and, still journeying nothward, they soon reached a country that might well test their courage and faith in God. Before them lay the powerful and populous kingdom of Bashan, crowded with great stone cities that to this day excite the wonder of the world -- "three score cities.... with high walls, gates, and bars; besides unwalled towns a great many." [Deuteronomy 3:1-11] The houses were constructed of huge black stones, of such stupendous size as to make the buildings absolutely impregnable to any force that in those days could have been brought against them. It was a country filled with wild caverns, lofty precipes, yawning gulfs and rocky strongholds. The inhabitants of this land, descendants of a giant race, were themselves a race of marvellous size and strength, and so distinguished for violence and cruelty as to be the terror of all surrounding nations; while Og, the king of the country, was remarkable for size and prowess, even in a nation of giants.

The answer regarding the age of the earth varies, depending on the opinion sought after.
The Evolutionist will tell you that the earth is millions of years old, based on certain assumptions or theories which cannot be scientifically proven. Time is added as the substantiating factor to provide a possibility of occurrence. The addition of "time" adds nothing to anything in this world except ageing, and with ageing brings decay.
The Annals of the World: James Ussher's work was originally published in Latin in the 1650's. Ussher devoted himself to the defense of the Christian faith. Born in Dublin, Ireland 1581, this highly educated, well travelled historian, devoted several years to writing a history of the world from creation to 73AD. According to Ussher the earth had an age in years of 4076c AM, 4786 JP, in 73 AD.
AM (Anno Mundi) Years of the world from creation (a=autumn, b=winter, c=spring, d=summer)
JP (Julian Period) Year starting from January first 4713BC.
This would today give us an age of the earth of 6,719 years in 2005.
The Illustrated Chart of History. Sebastian C Adams (1825-1898) was an ardent student of history, and in 1861 he began the project which was to gain him world fame - The Illustrated Chart of History. It took 25 men 10 years to research, write and illustrate this major work, which covered nearly 6000 years of recorded history. The chart gives a period of 4004 years from creation until the birth of Christ and concludes in the year 1900AD. This would today give us an age of the earth of approximately 6010 years in 2005.
Creation scientists usually give us an age of the earth of up to 10,000 years.

"Before the flood, dinosuars and man lived together on the planet. Extinction of the great marine reptiles, along with the majority of all other types of marine creatures, would have been caused by the violent upheavels of the Flood. , many being buried and preserved as fossils.
Two of each kind of land dwelling dinosaurs survived by being taken into the Ark. After the flood they faced a radically different and more hostile world, and became extinct, along with countless other less spectacular creatures, some time after. There is some evidence that men new about dinosaurs, for a short time (perhaps several centuries after the Flood) before they finally became extinct. The descriptions of behemoth (Job:14.15) and leviathan (Job:41.1) quite possibly refer to some of the few post-Flood giant reptiles still in existence at the time."

In Genesis 7:11-12 the Bible states that the water came from:- ".... the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.
And the rain was upon the earth forty days and forty nights.

"This whole dating method is dependant on knowing what the C14/C12 ratio was at the time of the organism's death. The value used is based on the assumption that C14 in the atmosphere was long ago built up to a steady state, that is the amount entering the atmosphere is in balance with the amount leaving by decay. The fact is that modern measurement show that C14 is still building up rapidly, and this would mean that the whole atmosphere is much less than (approximately) 30,000 years old. This would also have the effect of making C14 ages artificially older, especially the older dates. There are a number of other effects which would increase this tendency.
Page 12 "The Answers Book" by Ken Ham, Andrew Snelling, Carl Wieland.