Existing AS numbers are 32-bit, but sure, 24 is probably enough. The problem is with 64-bit addresses you'd only have 40 bits left for the whole AS. They'd qui

Existing AS numbers are 32-bit, but sure, 24 is probably enough. The problem is with 64-bit addresses you'd only have 40 bits left for the whole AS. They'd quickly run out if they gave each customer a 32-bit block, so they'd have to use 20-bit blocks or so. Then you have corporate customers who want to do complex internal subnetting, for which 20-bit wide blocks are administratively burdensome. 10.0.0.0/8 is 24-bit and they already run into problems there. They start having to use variable-sized subnets because the main office needs a 14-bit wide block but you don't have enough addresses to give every office that many, and then you have to renumber any time the size of an office changes, and probably renumber two other offices to free up a large enough contiguous address block. That all goes away if you can give every customer billions of addresses and they don't have to worry about their subnets being "too big" which means they never end up being too small.