Is the ministry of the tabernacle for ages 30 to 50, or for ages 29 to 49?

Question

From Numbers 4:

1 And the Lord spake unto Moses and unto Aaron, saying,

2 Take the sum of the sons of Kohath from among the sons of Levi, after their families, by the house of their fathers,

3 From thirty years old and upward even until fifty years old, all that enter into the host, to do the work in the tabernacle of the congregation.

The thirty to fifty age range is repeated multiple times over the course of the chapter, and has been understood to be the origin of the custom that a man was expected to be 30 years of age to begin a ministry (including an application in reckoning the chronology of John the Baptist and Jesus).

Sometimes Jewish chronology counts inclusively -- e.g. "the 30th year" is the time between one's 29th birthday and 30th birthday. Sometimes they do not count inclusively. In this sense "30 years of age" could refer to 29 years old or to 30 years old.

Is there any indication that the work of the ministry began in the 30th year vs at age 30? And that retirement took place at age 49 vs age 50? (or even 51)

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Addendum for clarification

This question is not about the Numbers 8:24 reference to duties at age 25, though in theory the same question could be asked of it--whether 25 means 25th year (24 years old), or 25 years old.

Answer 1

This is my understanding.

1. The Kohathites were responsible for the care of the holy things in the tabernacle like the incense stand, showbread, menorah... and the items used for sacrifices (plates, dishes, bowls, firepans, meat forks, shovels, and sprinkling bowls) see Numbers 4:1-17 (Age Group 30-50)
2. The Gershonites carry the curtain, Items of the Tabernacle, They carry the Tabarnale when the Israelites moved from the plan to place (Age Group 30-50) see Numbers 4:21-28
3. The Merarites carry the surrounding strur=tures and the beams and bars, pgs that are used to erect the strutures. (Age Group 30-50) see Numbers 4:29-33
4. The children of Aron are the priests. No one else can be a priest
5. In Exodus 8:24 the verse indicates that the Levites start at 25 and undergo training and their actual works starts after 5 years
6. It is the completion of 30 years and completion of 50 years that is used.

Exodus 8:24 This is [the rule] concerning the Levites: From the age of twenty-five years and upwards, he shall enter the service to work in the Tent of Meeting. Hope this helps a bit.