I think it is actually 128bit. Each character in the address is a hexadecimal digit, and represents 4 binary digits.
Hex -> Bin
0 -> 0000
1 -> 0000
...
E -> 1110
F -> 1111
So your example:
2001:0000:0000:0234:001c:4350:0001:ae1f (HEX-base16)
Translates to:
0010 0000 0000 0001:0000 0000 0000 0000:0000 0000 0000 0000:0000 0010 0011 0100:
0000 0000 0001 1100:0000 0000 0000 0001:0100 0011 0101 0000:1010 1110 0001 1111 (BIN-base2)
8 * 4 * 4 = 128 ((8 groups) * (4 nibbles/group) * (4 bits/nibble))
or if you are assuming every 2 characters represents 0-255 decimal, the equation would be:
8 * 2 * 8 = 128 ((8 groups) * (2 bytes/group) * (8 bits/byte))
-genius_at_work
