Don't go by how long you have stored the yeast (assuming that was what you meant by "a year old"), use the packet date code. You can check the Mr Beer yeast by the packaging date code on the packet day and year, formatted DDDYY. My last Churchill NB Ale end of life can had a 2016 dated yeast. I did substitute a different yeast (London ESB). I did throw the can yeast in the boil.
However, you have to figure that Mr Beer would package yeast that would still be viable enough by the HME best-by date. You also have to consider though if it has a viable low number of yeast cells, then it will be in growth phase longer and will make much more flavoring which may not be what you want. As mentioned above, if you do use the can yeast and get no action in a day or 2 you can put a newer yeast in as well.
that's the info i needed. i've made 4 batches of mrb extract, and a few using extract and grain. i still use an ice chest and frozen bottles for temp control. i've been very happy with the beer so far. thanks So much for your input....i hope the yeast works... i'll know tomorrow.