I can't really add any personal experience to this as aside from a very small number of accidents mostly when ill the only times I wet the bed was fully on purpose and that mostly stopped once I was able to consistently buy nappies whenever I wanted them as it was easier to clean up and hide the evidence.
I was however, actually doing a little bit of research and reading on this personally just this morning, so here is what I found.
From various studies conducted by different medical bodies (like the UK's NHS) it seems that children who are able to be completely dry without any issues are generally potty trained and dry at night by around age 4-5. Studies have shown that around 21% of 4 and a half year olds wet the bed less than twice a week and only 8% wet more than that, meaning 29% still wet the bed and 71% are dry at night by 4 and a half.
Some may take a little longer to be completely free of night wetting but the majority are mostly dry at night by about 4 and a half having maybe 2-4 accidents a month until around 5 years.
It is recommended by most bodies that if a child is still having 1 or 2 wet nights a week after the age of 5 to have them see a doctor in case of medical causes.
For those who do have a little more of a problem gaining control it is estimated (going from medical records) that around 15% of all children between the age of 5 and 10 will experience some degree of bedwetting. This number tends to vary by country for example in the USA the estimate is 15% in the UK it is 8-10%, by the age of 15 the estimates of children still wetting the bed regularly (even just once or twice a week) drops down to about 2-3%.
Various environmental, social and economic factors seem to impact this figure and the actual percentage may be higher as some families may not report it to their doctor so it never reaches their records.
To put that into perspective the UK has, at the last record update, around 10 million children in the school system (up to 16 years) 5.5 million of which are in primary school (ages 4-10). Using those percentages would mean in the UK alone possibly as many as 550,000 children between 5 and 10 still wet the bed regularly and 200,000 are still wetting the bed by age 15.
Studies also show that bed wetting tends to affect slightly more boys than it does girls with around 65% of records being for boys.
Studies also seem to show that children who are still wetting the bed more frequently than two or three times a week by the age of 8 are more likely to still have a problem by the age of 15 and onwards. While children who are able to get almost completely dry nights before that may or may not experience a relapse later on in their childhood especially in their early teens as hormones and other physiological changes happen. They are also more likely to be able to keep that dryness and control into adulthood.
Given that estimates are 1-2% of adults still experience nocturnal enuresis and between 5-20% of adults, depending on location, suffer from UIC it seems quite likely that most of the children who have not been able to stay dry at night by the age of 15 are likely to remain as bed wetters well into adulthood, joined by others who develop IC past their childhood.
I was unable to find any studies correlating UIC and nocturnal enuresis in adults to childhood bed wetting, but I also wasn't looking too deeply, I am sure studies like this have been carried out but they are buried deeper than a couple hours of poking around will produce.
