var yearSuffix1 = "лет";
var yearSuffix2 = "год";
var yearSuffix3 = "года";

bool isYearSuffixIsFirst = remainderOfDivisionBy10 == tenDividerThresholdLow ||
                           remainderOfDivisionBy10 > tenDividerThresholdHigh ||
                           (remainderOfDivisionBy100 >= hundredDividerThresholdLow &&
                            remainderOfDivisionBy100 <= hundredDividerThresholdHigh);

string yearSuffix = isYearSuffixIsFirst
    ? yearSuffix1
    : remainderOfDivisionBy10 == 1
        ? yearSuffix2
        : yearSuffix3;