What's the ideal amount of savings that a 25 year old should have?

There's no ideal. It depends on what you're doing. If you're still a student, your ideal would be different than if you had just started work/if you have worked for a few years already. You should plan backwards instead. When do you hope to get your next big ticket item by? Calculate how much you'd need and how long you'd need to reach that amount. If you're on track, then it's ideal.

Depends on when you start work, your pay and expenses. Everyone situation is different.