To Calculate someone's age using a program.

To calculate someone's age using a program, you can follow these steps:

1. Ask the user to input their birth date in a specific format (e.g. DD/MM/YYYY).

2. Split the input into day, month, and year variables.

3. Get the current date using the system's time and date functions.

4. Split the current date into day, month, and year variables.

5. Calculate the difference between the current year and the birth year.

6. Check if the current month is less than the birth month. If so, subtract 1 from the age calculated in step 5.

7. If the current month is equal to the birth month, check if the current day is less than the birth day. If so, subtract 1 from the age calculated in step 5.

8. Output the calculated age.

Here is an example code in Python:

```python

import datetime

birthdate = input("Enter your birth date (DD/MM/YYYY): ")

day, month, year = map(int, birthdate.split('/'))

current_date = datetime.date.today()

current_day = current_date.day

current_month = current_date.month

current_year = current_date.year

age = current_year - year

if current_month < month or (current_month == month and current_day < day):

    age -= 1

print("Your age is", age)

```

Note: This code assumes that the user will input the birthdate in the correct format (DD/MM/YYYY). Additional error handling can be implemented to validate the input format and handle invalid inputs.