Answer: Clivias like to be pot bound--it could be that your 3-year old plant is happier because its roots are filling out the pot better! Also, prolonged sun exposure can cause leaf scorch--the plant prefers just a few hours of direct sun, preferably in the morning, with bright light without direct sun for the rest of the day.
Could you be overwatering your 2-yr old plants? Perhaps the soilless mix is holding a little too much water--the older one, being more pot bound, has less soil and therefore holds less water. Dry leaf edges are commonly a sign of overwatering--but it could also be over fertilizing, underwatering, inadequate humidity, or pests. It's hard to know for sure!
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