age_guess2ndver.py

# Step 1
# Ask the user for their name and the year they were born.
name = input("What should I call you? ")

while True:
    birth_year = input("What year were you born? ")
    try:
        birth_year = int(birth_year)
    except ValueError:
        continue
    else:
        break

# Step 2
# Calculate and print the year they'll turn 25, 50, 75, and 100.
current_year = 2017
current_age = current_year - birth_year
turn_25 = (25 - current_age) + current_year
turn_50 = (50 - current_age) + current_year
turn_75 = (75 - current_age) + current_year
turn_100 = (100 - current_age) + current_year

# Step 3
# If they're already past any of these ages, skip them.
if turn_25 > current_year:
    print("You'll turn 25 in the year {}, {}".format(turn_25, name))
if turn_50 > current_year:
    print("You'll turn 50 in the year {}, {}".format(turn_50, name))
if turn_75 > current_year:
    print("You'll turn 75 in the year {}, {}".format(turn_75, name))
if turn_100 > current_year:
    print("You'll turn 100 in the year {}, {}".format(turn_100, name))