Blasted urban myths.
We have been told time and time again how stable MDMA-HCl is. Now whilst i have no data to back me up, an examination of the structure of Meth-HCl would lead me to believe it is MORE stable than MDMA. Yes it is more hygroscopic but that issue is easily avoided.
IMO it will keep for a long long time - if its in its "ice/rock" form likely even longer as its far purer and more dry to begin with. Provided it is stored as stated above, in a sealed, dry container out of light it will probably still be just as active by the time u have a spouse, mortgage and kids.
The freezer urban myth has originated imo due to the "paste" style stuff larger DDs generally get when they are not getting "ice as in meth".
You know the type, very pastey, clumpy, sticky etc.
This generally is stored in the freezer because it is so full of moisture and solvents. By freezing it the water and solvents freeze also and the stuff is far more manageable and crystalline looking - leave it out for any length of time and it begins to go sticky and gluggy again as the liquid components melt - nothing is happening to the meth.
(of course anyone with half a brain would know drying the meth overnight spread out over a plate, with a bowl as a cover will get rid of this, and then allow it to be stored as you would normally do without the need for any freezing)