Remember brother, Allah has his reasons for making humans the way we are today as apposed to the way he made us before.
It is true Adam was 90ft tall, the reasons Allah decided it best to create him like that only Allah will know. In the future, weAllah initially made humans may be 90ftvery tall again, in Allah we trust and he always knows bestmankind has been decreasing in height ever since.
The Prophet said, "Allah created Adam, making him 60 cubits tall. When He created him, He said to him, "Go and greet that group of angels, and listen to their reply, for it will be your greeting (salutation) and the greeting (salutations of your offspring." So, Adam said (to the angels), As-Salamu Alaikum (i.e. Peace be upon you). The angels said, "As-salamu Alaika wa Rahmatu-l-lahi" (i.e. Peace and Allah's Mercy be upon you). Thus the angels added to Adam's salutation the expression, 'Wa Rahmatu-l-lahi,' Any person who will enter Paradise will resemble Adam (in appearance and figure). People have been decreasing in stature since Adam's creation.
(Translation of Sahih Bukhari, Volume 4, Book 55, Number 543)