The spiritual age of a person differs from physical age. In real life one may be nearing the end, about to die but spiritual age may be zero. Why?
Anyone not interested in spirituality and has yet to embark on a spiritual journey; the spiritual age of such person would always be zero.
One may be very young yet quite advanced in spirituality; the spiritual age of such a person would range between 95 and 99 for at 100 the soul atman having become pure finally liberates forever.
Swami Vivekananda an accomplished spiritualist did not want to gain enlightenment even though he could have easily done so under able preceptorship of his guru Sri Ramakrishna Paramhansa.
In the next manifestation he would definitely gain enlightenment but at birth also he would possess a spiritual age ranging 90 to 95.
Acharya Rajneesh (née Osho) was also an accomplished spiritualist who could have gained enlightenment in his lifetime but only for this dillydallying, mixing sex with yoga in the later stages of his life.
An avatar of his era Lord Krishna would have possessed at birth spiritual age ranging between 98 ~ 99. Spiritual age of 100 indicates gaining enlightenment and finally moksha salvation.
In society both examples exist. The physical age of a person could be 90 and the spiritual age zero. This would happen in case of religious practitioners having nothing to do with spirituality.
For those indulging in spirituality the physical age may be 40 but possess a spiritual age of 90.
The spiritual maturity is easily recognizable. One becomes master of scriptures, sacred texts. For one spiritually matured everything contained in sacred texts becomes like ABCD.