String generate(int age) {
   int age = list.get(position).getAge();
   int lastChar = Integer.parseInt((""+age).substring((""+age).length()-1, (""+age).length()));
   String old = "";
   if (age==11) old = "лет";
   else if((""+age).endsWith("1")) old = "год";
   else if(age>11 && age<15) old = "лет";
   else if(lastChar>1 && lastChar<5) old = "года";
   else old = "лет";
   return old;
}

int ageLastNumber = age % 10;

String old = "";
boolean exclusion = (age % 100 >= 11) && (age % 100 <= 14);

if (ageLastNumber == 1)
    old = "год";
else if(ageLastNumber == 0 || ageLastNumber >= 5 && ageLastNumber <= 9)
    old = "лет";
else if(ageLastNumber >= 2 && ageLastNumber <= 4)
    old = "года";
if (exclusion)
    old = "лет";

=0 означает ноль;
=1 соответствует ровно 1;
one - 21, 31, 41 и так далее;
few - от 2 до 4, от 22 до 24 и так далее;
many - 0, от 5 до 20, от 25 до 30 и так далее;
other - для всех прочих чисел (например, дробных).

int age = 5;
int ageLastNumber = age % 10;
boolean exclusion = (age % 100 >= 11) && (age % 100 <= 14);
String old = "";

if (ageLastNumber == 1)
    old = "год";
else if(ageLastNumber == 0 || ageLastNumber >= 5 && ageLastNumber <= 9)
    old = "лет";
else if(ageLastNumber >= 2 && ageLastNumber <= 4)
    old = "года";
if (exclusion)
        old = "лет";

System.out.println(old);

public static StringBuilder appendAge(StringBuilder, int age) {
   assert age > 0 : "Age must be a positive number";
   double[] limits = {0, 1, 2, 5};
   String[] strings = {"лет", "год", "года", "лет"};
   ChoiceFormat format = new ChoiceFormat(limits, strings);
   int rule = 11 <= (age % 100) && (age % 100) <= 14 ? age : age % 10;
   return builder.append(age).append(' ').append(format.format(rule));
}