Having an offer from infosys and bilvantis(startup)

If the startup is even a bit stable join that, the younger you are, more risks you can afford Later as you age, you won't be able to Ensure the startup is stable not just a new one opened to gather funding

Join who is giving higher package as your experience is less. If you join in Infosys hikes won't be much so I prefer start up is better and after getting better hikes you can shift again

What they offer? I mean salary

Job security is a myth now. So join startup upskill and jump again

Join Infosys if looking for job security.

If you don't have any financial commitments, i would say go for a startup but since you mentioned it's just 5 years old, read reviews and gather ex employees feedback over LinkedIn or somewhere then think twice and decide.

Even though I'm in the same situation slightly different, infosys offered me more so choosing this