Well, I'm not too sure but I think the only way you can make the growth faster is by de-bugging it(if this is even possible on the V5.5). But be VERY careful if you're that desperate. You can BREAK your tama BEYOND repair if you de-bug it incorrectly. Then, even if you do de-bug your tama, it will speed up the growth process, but you can't make it slow down again. It is a permanent result of de-bugging. If you want my opinion, don't try it. There's a huge risk you could break your tama. If you're that desperate, it's your choice but don't try to do it without instructions. Search this site or google de-bugging a V5.5. Like I said, I'm not exactly sure you can de-bug a V5.5 though, it may not be possible.
Anyway, hope I helped!