How soon we can renew British passport

[AliAla]

Apologies in advance if this is a repeat post or sent under the wrong category.

My query is - How soon we can renew the British passport? Reason - I read somewhere that after 50 years of age, the passport is issued for 5 years rather than 10 years. If that is the case - I will be 50 in 3 months and my password is expiring in August'26. Can I apply now so that I can get the validity for 10 years?  

Thanks in advance for any advice on this.

[CR001]

There is no such rule. You have either misread or it is relevant to another country passport.