Was 30 the canonical age for Catholic priesthood in the 1700s? I understand that the current canonical age for Catholic ordination is 25 years. Was the minimum previously 30 years?

The documentation of a priest's ordination in 1775 shows that the diocese spent some time examining the age of the applicant. At issue was whether he, a "cleric of minor orders", was old enough to join "the Order of the Presbyter". A note up front on the document reads "older than 30 years". In letters, the applicant declared that he was 31 years of age, while one official noted that he appeared more like 24. In the end he was ordained. The example is from the historic archives of Durango, RGHC AHAD-120, p. 561.
The Council of Trent (1545-1563) wrote a decree Sacrificium et sacerdotium on the holy orders dealing with this question:

Nullus  in  posterum  ad  subdiaconatus  ordinem  ante  vigesimum  secundum  ad  diaconatus  ante  vigesimum  tertium  ad  presbyteratus  ante  vigesimum  quintum  aetatis  suae annum promoveatur.
Sciant tamen episcopi non singulos in ea aetate constitutos debere ad hos ordines assumi sed dignos dumtaxat et quorum probata vita senectus sit.
Regulares  quoque  nec  in  minori  aetate  nec  sine  diligenti  episcopi  examine  ordinentur; privilegiis quibuscumque quoad hoc penitus exclusis.
(Decretum super reformatione, canon XII)
No one shall for the future be promoted to the order of subdeaconship before the twenty-second year of age; to that of deaconship before his twenty-third year; to that of priesthood before his twenty-fifth year.
Nevertheless, bishops are to know, that not all who have attained to that age must needs be admitted to the aforesaid orders, but those only who are worthy, and whose commendable life is an old age.
Regulars likewise shall not be ordained under the above age, nor without a diligent examination by the bishop; all privileges whatsoever in this regard being completely set aside.
(Decree on reformation, chapter XII)

So the minimum age for ordination as a priest was set to 25 years. The diligent investigation of the age was prescribed in canones V and VII.
I do not know for sure, if there was a later papal decree raising the minimum age, but I do not see any reason for such a step. There could also be a local law setting a higher age.
So probably the minimum age for your case was 25. So the suspected age of 24 would have been a problem. Maybe the note &quot;older than 30 years&quot; refers to the declared or the investigated age.