A series of studies we conducted regarding the age at which people accept Christ as their Savior highlights the importance of having people invite Jesus into their heart as their Savior when they are young. We discovered that the probability of someone embracing Jesus as his or her Savior was 32 percent for those between the ages of 5 and 12; 4 percent for those in the 13- to 18-age range; and 6 percent for people 19 or older. In other words, if people do not embrace Jesus Christ as their Savior before they reach their teenage years, the chance of their doing so at all is slim.
The importance of building strong spiritual foundations at an early age is again confirmed by recognizing that in 2003, there was virtually no difference between the spiritual standing of adults and those exiting their childhood years. Specifically, 4 percent of 13-year-olds were evangelicals compared to just 6 percent of adults; 34 percent of the 13-year-olds were born again, which was slightly less than the 38 percent found among adults. In other words, by the age of 13, your spiritual identity is largely set in place. Thousands of people decide to embrace Christ as their Savior each year, but from a statistical vantage point the number of Christians is not increasing—the new believers are essentially replacing the Christians who died or those who renounced their faith in Christ. My tracking of religious beliefs and behavior for more than a quarter century has revealed that the spiritual condition of adolescents and teenagers changes very little, if at all, as they age. When significant change is evident, it usually is attributable to a dramatic intrusion of the Holy Spirit into their lives.
Barna, George (2003). Transforming Children into Spiritual Champions (p. 34). Gospel Light Publications. Kindle Edition.