The general pattern is that the older a person is, the more likely they are to attend religious services. However there are two exceptions to this:
1) 15 and under: more likely to go because they are made to do so by parents
2) 65+: more likely to be sick or disabled and thus unable to attend. In the past, higher death rates have also made this a smaller group, reducing the total number.
Voas and Crockett argue that there are two main reasons for age differences in religious participation:
1) The ageing effect: people turn to religion as they get older. As we approach death, we become more concerned about spiritual matters and the afterlife, repentence of past deeds etc.
2) The generational effect: as society becomes more secular, each new generation is less religious than the one before. Thus, there are more old people than young people in church because they grew up at a time when religion was more popular.