The minimum age requirement for starting an online equity trading account can vary depending on the regulations and policies set by the financial authorities and the brokerage firm or financial institution you are dealing with. In India, the Securities and Exchange Board of India (SEBI) has set the minimum age requirement for opening a demat and trading account at 18 years old.

Therefore, to have an equity trading account opening online with Sarthak Investment, a leading provider of demat account opening online, you would generally need to be at least 18 years old. It's important to note that age requirements may differ based on the jurisdiction and the specific brokerage firm's policies. It's always recommended to check with Sarthak Investment directly to confirm their specific requirements and guidelines for opening an online equity trading account based on your age.