Kelsey turned 25 in 1999. Her older sister was born 3 years before Kelsey. It's currently 2021. How old is Kelsey's older sister? Think carefully first, then make a decision:
Kelsey turned 25 in 1999 so she was born in 1999 - 25 = 1974. Kelsey's sister is older by 3 years so she was born in 1974 - 3 = 1971. It's currently 2021 and Kelsey's sister was born in 1971 so she is 2021 - 1971 = 50 years old. So, the answer is 50.