C#, 1 line
Complexity\n- Time complexity: O(n)\n\n- Space complexity: O(1)\n\n# Code\n\npublic class Solution \n{\n    public int CountSeniors(string[] details) \n    {\n 
# Complexity\n- Time complexity: $$O(n)$$\n\n- Space complexity: $$O(1)$$\n\n# Code\n```\npublic class Solution \n{\n    public int CountSeniors(string[] details) \n    {\n        return details.Count(d => int.Parse(d.Substring(11, 2)) > 60);\n    }\n}\n```
['C#']