50-60 years for 5th gen is a bit stretch.
Tejas is not even in three digits after 40 years in development and production. I highly doubt AMCA without an engine option today will be in flight tests before 2035 (remember 2035 is now just 10 years away). Then another 10 years of integration and testing. Four or five round of redesigns to remove all issues or integrate a new engine if India gets a reliable supplier and 10 years of certification. We are not looking 2065 before a final version of AMCA ready for flight becomes available. Another 20 years to produce 4-5 squadrons given broken Indian supply chains.
60 years easy. 50 is generous.
India certainly has few options but those might require it to be relegated in the geopolitical order - not that it is faring well right now.
Its not geopolitics as much no one is making a platform that India needs. Actually, only options right now are China and USA.
India needs a platform that has legs to take fight into Chinese airspace -- thats why it needs fifth gen fighters in first place. Nothing on market has one that can fly over himalaya and India air space, into china and come back in all stealth configuration. Basically, there is no J-20 on sale right now.
Then there is question of integration. India needs integration with Isaeli and Indian EW/AEW&C platforms. It needs integration with Russian, Israeli and Indian made weapons, housed internally.
No one has such a plane, no one has plans to make such a plane, no one has a plane that can be adapted into such role.
So Indian fifth gen fighter is dead in water for 50-60 years.
IAF had a good time when Su-27 design based fighter was available, customizable and dominant. With Russia out of the game, that option for fifth gen has gone. I do not see Russia entering in the game anytime soon, if ever.