Happy New Year 2010.
There is no spiritual meaning of being adult.
This has a legal meaning only - reaching the age of 18 years.
Being grown up can be taken up & discussed spiritually.
In our ancient Social & Spiritual System, there were 4 ASHRAMS - BRAHMACHARYA ASHRAM, GRAHASTHA ASHRAM, VANPRASTHA ASHRAM & SANYAS ASHRAM.
After birth, when a child gets the age of little understanding, from then his/her education starts. That time he/she has to concentrate on the education giving full respect to his/her Guru Ji. This was 1st one.
Then he/she enters into the 2nd - the Grahastha Ashram - Marriage, Social Involvements, Responsibilities towards Family, Society, etc.
THe 3rd one - Vanprastha - Being in family, he diverts his attention from BHAUTIK to ADHYATMIC - towards Spirituality - towards religion - towards the Almighty.
The 4th one - Leave all the MOH - all the belongingness - cut all the cords which bind you with this BHAUTIK world, and devote fully towards that SARVASHAKTIMAN PARAMESHWAR - this is the best time, which a person utilizes only for himself/herself - for his/her advancement, betterment, upliftment, for achieving the PARAMATMA.
Aum Namah Shivay