mitsho
Deity
1. Your cognitive capabilities begin declining multiple decades before you turn 80
2. You grew up in a completely different time and can't relate to the people who are growing up today at all
3. You worked your day job career many decades ago and can't relate to the people who are trying to make ends meet today at all
4. Your moral compass was finetuned multiple generations ago. You are out of touch with the rest of the country to some degree.
5. You could break bones and/or get worse injuries just by falling over.
6. A leader who is close to death doesn't seem like a good idea. Having to replace a leader who died creates instability
6 problems just off the top of my head. The main one is that the younger and working classes are experiencing huge problems. Ideally the person leading the recovery should have some sort of connections to issues like that and some first hand experience with what they are going through.
You missed the most obvious point: He/she DESERVES to retire at 80 years old. It's a demanding job and work-life balance is important. No one is indispensable, and at 65 usually (depending on your job it can go up to 70-75 I'd say, but also down for more physically demanding jobs) you should not need to work anymore. All the other points about leading a country etc are true as well, but how can you enforce a retirement age when your politicians don't care for it?