[Mr. K]

I was wondering about that too- at the beginning he did the ‘birthday bacon’ thing saying his age was 52....

Then, later, in either the same episode or another one, they had his wife doing the bacon thing saying he was 51... so was that a foreshadowing of something coming up on his NEXT birthday? (plus his hair was grown back)

They have had some great foreshadowing in some of these episodes and some confusing, not so great ones

[E. Pluribus Unum]

The opening scene of season 5 (the current season) was a flash-forward to a Denny's on Walter White's 52nd birthday where he buys a SAW machine gun.

Then right after the Breaking Bad intro screen we come back to present day, meaning the period right after the end of the fourth season, just prior to his 51st birthday. Mike is still in Mexico and hasn't heard about Gus's murder yet, so it's just days after the poisoning and shootout with the cartel.

We don't know what happens to get him to the point of needing a machine gun a year later, but we know it can't be good. Plus, he's coughing, so the implication is that the cancer has come back.