As the error suggests, using the + operator for concatenation is only valid if both sides are strings. Python uses string formatting instead of concatenation when mixing strings and variables. In modern Python (3.6+), your example can be simplified using f-strings:

name = "Alice"
age = 25
message = f"My name is {name} and I am {age} years old."
print(message)

This format is easier to read, and avoids the TypeError. Prior to Python 3.6, you would have needed to use the % operator and sprintf-style formatting:

name = "Alice"
age = 25
message = "My name is %s and I am %d years old." % (name, age)
print(message)

In addition to the official Python docs linked above, there is also a good tutorial at Real Python that discusses these techniques in more detail.