The main source of information for suicide in England & Wales is ONS.
The National Statistics definition of suicide is deaths where the underlying cause of death was either X60-X84 (Intentional self-harm) or Y10-Y34 (Injury/poisoning of undetermined intent).
In the UK, a coroner is able to give a verdict of suicide for those as young as 10 years. However, rates per 100,000 are provided by the ONS for ages 15 years and over when their suicide bulletin is released. This is due to the known subjectivity between coroners with regards to classifying children’s deaths as suicide, and because the number in those under 15 tends to be low and their inclusion may reduce the overall rates. NISRA and NRS, however, do provide rates from as young as 10 years and rates for all persons, males and females are based on all ages.
You can read various suicide and mortality statistics for the UK below: