Here's a possible pseudocode algorithm that prompts the user to enter their name, age, and registration number, and then prints out their details:
// Prompt the user to enter their name, age, and registration number
print("Please enter your name:")
name = read_string()
print("Please enter your age:")
age = read_integer()
print("Please enter your registration number:")
registration_number = read_string()
// Print the student details
print("Student Details:")
print("Name: " + name)
print("Age: " + age)
print("Registration Number: " + registration_number)
Note that this pseudocode assumes the existence of functions or commands for reading input from the user (such as read_string() and read_integer()), which may vary depending on the programming language or environment being used.