Handling null-safety Exceptions in Dart - dart

Question

In this simple dart exercise, I was trying to handle the exception for the null safety in Dart.
However, I think the code below is not following DRY principles. Will be glad if anyone can correct me.
void Exercise1() {
/// declared these as global variables for availability to all blocks.
int? age;
String? name;
stdout.write('What is your name? ');
name = stdin.readLineSync();
/// This do-while block will validate: name is not empty or less than 3 char.
do {
stdout.write('What is your name? ');
name = stdin.readLineSync();
} while (name == null || name.isEmpty);
/// This de-while block will validate that age is entered and not -ve value.
do {
stdout.write('Hello $name, What is your age? ');
age = int.tryParse(stdin.readLineSync().toString());
} while (age == null || age.isNegative);
/// This expression computes the age left till 100 years.
int? yearsToHundred = 100 - age;
/// This prints out the results.
print(
'\nHey $name, your are $age year of age now. \nYou will be 100 years in another $yearsToHundred years time. \nEnjoy your life to the fullest, Cheers!');
}
What I want here is to validate and check if the number is null, the length is not zero, and only numbers are entered at the prompt. Otherwise, keep looping the input statement till valid input is provided.
void Exercise2() {
String? number;
do {
stdout.write('Enter a number: ');
number = stdin.readLineSync();
} while (number == null || number.length == 0);
int? num = int.parse(number.toString());
if (num.isEven) {
print('Even');
} else {
print('Odd');
}
}