I would currently be 4*4=<<4*4=16>>16 years old, since I'm 4 times older than Billy's age of 4.

Therefore, in order to find my age at Billy's birth we'd simply subtract Billy's age of 4 from my age, meaning I was 16-4= <<16-4=12>>12 years old

# Answer

12
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If I'm 4 times older than Billy currently, and Billy is 4 years old, how old was I when Billy was born?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
12
If I'm 4 times older than Billy currently, and Billy is 4 years old, how old was I when Billy was born?
train