I made a breakthrough when I found a baptism for my ancestor taking place when she was 18 years old. I have also heard of people getting baptised in their 20s. I know it's not unusual now, with some free churches going in for adult baptism, but in the 18th and 19th centuries it was not the norm. Golden rule of genealogy - whenever you have enough evidence to suggest that you have found a pattern that obeys a rule, you can guarantee that the first time you need to apply the rule, it will not hold true.