I relied on a system to prolong my life in ancient times.

This is a fantasy/time-travel/system/farming/infrastructure-building story. The male protagonist, Xiao Siyue, is born late in the day and transmigrates into the body of a newborn baby. She's premature, sickly, and doctors predict she won't live past ten. Luckily, she has a system that allows her to extend her life by signing in daily and completing tasks to earn merit. So, she doesn't hesitate to make money, build infrastructure, and develop agriculture. Xiao Siyue excitedly exclaims, "System, if I keep doing tasks and earning merit, I can live forever!" The system replies, "Host, I think you're dreaming..."