I think it's weird having an arbitrary minimum age to be president. I would probably never vote for someone in their 20s anyway, but I don't think there should be a legal barrier. In my country (Brazil) it's the same age, but we usually just copy US in think kind of policy. I wonder how common it's in the rest of the world.
I'm more bothered by the geriatric politicians in various democracies than I am that you're missing out on some amazing politician in their twenties.
The UK has a practical minimum of 18 for Prime Minister (technically there is no minimum but practically there is) but realistically never elects a PM under 40.
For British Sovereign there is also no limit, any particularly young Sovereign has effectively delegated to a council of regents historically. In practice this is also unlikely - although in theory of course we are two untimely deaths from a 12 year old taking the throne.
