I tend to vary, for times that are within a couple months of RL time, I refer to time passing 1:1 with RL, for times greater than that, I typically refer to time in BM passing as if it were about 4 times as fast as RL.
Also among Sangius Astroism on Dwight, there is a tendency to consider each four seasons one year, due to saying that elections that take place in the church every six RL months are taking place every two years.
I think our characters age about a year for every four seasons, but it's not exact because there are a lot of factors that affect age. And I may be wrong anyways.
That said, there's no real right way, but I'm sure people will tell you their way is the only right way. But hey, whatever floats your own boat.