Four in 10 HDFC Bank customers are under 40, giving one of India's biggest private lenders a younger customer base as it looks for future growth. The figure offers a glimpse into how banking habits are changing as more younger Indians enter the formal financial system.HDFC Bank said 22% of its customers are 30 years old or younger, while 42% are below 40. The lender said this creates an opportunity to engage with customers through their life cycle and build future business. The disclosure matters because customer age can shape demand for savings accounts, loans, cards, investments and digital services over time. A younger base can also give banks more chances to deepen relationships as incomes rise and financial needs change.Growth Engine"22% of our customers are actually 30 years of age, 42% are less than 40 years of age. This enables us an opportunity to engage through their life cycle, which would be the future engine of growth," Chief Executive Officer Sashidhar Jagdishan said.ALSO READ: 97% Of Transactions Are Digital. So Why Does HDFC Bank Have 9,700 Branches?The bank said it continues to add about 6 million to 8 million customers a year, taking its total customer base to 100 million. That funnel, management said, can support future expansion. Digital PushHDFC Bank linked its long-term strategy to technology and customer experience. The lender said its mobile app now serves more than 60 million registered users.It added that digital adoption has reached 97% for payments and service transactions, while 92% of acquisition journeys are now digital. Next Target Customers?The bank said its focus remains on return on assets, loan growth, deposit growth and balance-sheet quality, with the aim of delivering consistent earnings per share growth. A younger and expanding customer base is likely to remain central to that plan.ALSO READ: Banks Rake In Rs 19,083 Crore In Minimum Balance Penalties Over 3 Years; HDFC Bank Tops Chart