In the case of the Priesthood the individual is not expected to be economically independent with a stable job. In the case of the Diaconate a mas is expected to have a stable job. My guess is that the age limit of 31 is to ensure that the individual is somehow established professionally before being fully involved in the vocation. It is quite difficult to balance spiritual life and professional life and so at the beginning it is better to have quite a bit of experience at least in one of the two.
Given - as it is typically employed today. But, again, I am challenging that very sensibility. I neither think that the permanent diaconate ought to be thought of as a “married man’s vocation” primarily nor, necessarily, just as a sort of “second career” for men already established in other professions. While those are certainly noble calls and worthy ways of approaching the potential of the permanent diaconate which has, obviously, been exploited well over recent decades until today, it ought not be the ONLY way of employing this clerical state. Indeed, why should there not also be full time deacons in celibate ministry to complement the pastoral ministry of priests? (Or, even, many more full time married deacons whose only job is with the Church, for that matter.) I think that we are, therefore, missing both an opportunity for the Church and failing to foster the potential of certain vocations to this form of ordained ministry - especially from our youth - in limiting it as has generally been done.
I could see, however. where distinct norms for those who aspire to enter diaconal discernment in varying degrees of intensity for service or from unique states of life might be necessary, though. Or, perhaps not even, actually. It may, instead, just be a matter of individual prudence to tell certain men to “come back later” when a greater stability of their own lives is had which will enable them to be at a better place to pursue the possibilities and give the personal dedication necessitated responsibly.
So, IMO, let’s invite boys and young men to look at the potential of this call and not shut the doors to them until they are already older, as is now the case. Truly, pursuing a call to the diaconate, initially, may even lead some of them to desire continuing further onto priestly ordination, also!