Numbers 8:25-26 New International Version (NIV)
25 but at the age of fifty, they must retire from their regular service and work no longer. 26 They may assist their brothers in performing their duties at the tent of meeting, but they themselves must not do the work. This, then, is how you are to assign the responsibilities of the Levites.”
The Levites were to retire at age 50 so that the younger Levites would do most of the heavy lifting. There was heavy articles and furniture to move when moving the Tabernacle through the wilderness. The younger men did this. The older men helped the younger men learn their responsibilities. They were what we call mentors today. The older Levites would advise and counsel and the younger Levites gained more responsibilities. Do you have an older mentor in your life? Learn from your elders and give them respect. They have wisdom and knowledge to pass to you.