Maximum length for MD5 input/output

MD5 processes an arbitrary-length message into a fixed-length output of 128 bits, typically represented as a sequence of 32 hexadecimal digits.

• The length of the message is unlimited.

Append Length

A 64-bit representation of b (the length of the message before the padding bits were added) is appended to the result of the previous step. In the unlikely event that b is greater than 2^64, then only the low-order 64 bits of b are used.

• The hash is always 128 bits. If you encode it as a hexdecimal string you can encode 4 bits per character, giving 32 characters.
• MD5 is not encryption. You cannot in general "decrypt" an MD5 hash to get the original string.

See more here.