Package

To easily parse date we need package intl:

https://pub.dev/packages/intl#-installing-tab-

So add this dependency to youd pubspec.yaml file (and get new dependencies)

Solution #1

You can just simple compare years:

bool isAdult(String birthDateString) {  String datePattern = "dd-MM-yyyy";  DateTime birthDate = DateFormat(datePattern).parse(birthDateString);  DateTime today = DateTime.now();  int yearDiff = today.year - birthDate.year;  int monthDiff = today.month - birthDate.month;  int dayDiff = today.day - birthDate.day;  return yearDiff > 18 || yearDiff == 18 && monthDiff >= 0 && dayDiff >= 0;}

But it's not always true, because to the end of current year you are "not adult".

Solution #2

So better solution is move birth day 18 ahead and compare with current date.

bool isAdult2(String birthDateString) {  String datePattern = "dd-MM-yyyy";  // Current time - at this moment  DateTime today = DateTime.now();  // Parsed date to check  DateTime birthDate = DateFormat(datePattern).parse(birthDateString);  // Date to check but moved 18 years ahead  DateTime adultDate = DateTime(    birthDate.year + 18,    birthDate.month,    birthDate.day,  );  return adultDate.isBefore(today);}

The best age validation I have ever come up with is based on Regex.
The below logic covers all the breakpoint related age.

// regex for validation of date format : dd.mm.yyyy, dd/mm/yyyy, dd-mm-yyyyRegExp regExp = new RegExp(    r"^(?:(?:31(\/|-|\.)(?:0?[13578]|1[02]))\1|(?:(?:29|30)(\/|-|\.)(?:0?[13-9]|1[0-2])\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:29(\/|-|\.)0?2\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:0?[1-9]|1\d|2[0-8])(\/|-|\.)(?:(?:0?[1-9])|(?:1[0-2]))\4(?:(?:1[6-9]|[2-9]\d)?\d{2})$",    caseSensitive: true,    multiLine: false,  );//method to calculate age on Today (in years)  int ageCalculate(String input){  if(regExp.hasMatch(input)){  DateTime _dateTime = DateTime(      int.parse(input.substring(6)),      int.parse(input.substring(3, 5)),      int.parse(input.substring(0, 2)),    );    return DateTime.fromMillisecondsSinceEpoch(                DateTime.now().difference(_dateTime).inMilliseconds)            .year -        1970;  } else{    return -1;  }}void main() {// input values and validations examples  var input = "29.02.2008";  print("12.13.2029 : " + regExp.hasMatch("12.13.2029").toString());  print("29.02.2028 : " + regExp.hasMatch("29.02.2028").toString());  print("29.02.2029 : " + regExp.hasMatch("29.02.2029").toString());  print("11/12-2019 : " + regExp.hasMatch("11/12-2019").toString());  print("23/12/2029 : " + regExp.hasMatch("23/12/2029").toString());  print("23/12/2029 : " + regExp.hasMatch(input).toString());  print("sdssh : " + regExp.stringMatch("sdssh").toString());     print("age as per 29.02.2008 : " + ageCalculate(input).toString());}

Output

 12.13.2029 : false 29.02.2028 : true 29.02.2029 : false 11/12-2019 : false 23/12/2029 : true 23/12/2029 : true sdssh : null age as per 29.02.2008 : 12

I hope you will find this useful. :)

You can find year difference in following way.

String _data = '16-04-2000';    DateTime _dateTime = DateTime(      int.parse(_data.substring(6)),      int.parse(_data.substring(3, 5)),      int.parse(_data.substring(0, 2)),    );    int yeardiff = DateTime.fromMillisecondsSinceEpoch(                DateTime.now().difference(_dateTime).inMilliseconds)            .year -        1970;    print(yeardiff);