Short answer: That really depends.
Long answer: Descaling will be a function of how often you use your machine, age/type of the machine, and the quality of water you put in it.
Here in Adelaide where we have quite hard water (comparatively) I would typically descale my machine about every 2-3 ish weeks and i use it every day with 2-4 coffees per day. I have recently switched to using bottled water which means i can extend that to about every 4 weeks ish.
With my old breville BES800 in Brisbane was about every 2 months, with 1-2 coffees per day. Adelaide it was probably closer to 1 - 1.5 months.
It will also depend on how you descale. With my old breville I would use a 50/50 vinegar water mix, let the boiler heat up and run through 50/50 through the steaming iron and through the group head. Every second or third descale i would also use a mix of bicarb soda and water and do the same but do it first. Followed by a VERY VERY VERY thorough rinse of water and then vinegar.
I would say the descale on your machine is a good guide. If you feel it is too often then give it a little extra on the descale. The other alternative is that your machine is beginning to age and the boiler/heating unit is no longer as effective. Someone may know the inner workings of the unit, but I suspect the descale is prompted by a temperature differential between the heating element or water and the incoming water vs outgoing (or some variation of).
As a final note, a machine that does need a descale you should taste a fairly significant difference in the before and after in the quality of the shot. Let that be your number 1 guide to how often. If you notice a leap in quality of the shot taste wise, it was overdue. If you notice no difference then maybe it could have gone a little longer. Many of us however prefer to descale more frequently well before you would notice a reduction in shot quality.