My nine-year-old smells like a teen

My nine year old son’s school shirt smells bad like for an adolescent. His other clothes do not smell neither does his body; but when I smell his uniform shirt in the evening, it is terrible yet he bathes properly in the morning and evening. I even help him to bathe. He does not play football or participate in any other game. I also stopped him from riding his play bike because his arm muscles were developing like for a boxer. Has he started his adolescence at nine? please advise.

Worried mother.

As children grow up, they undergo many body and mind changes.
Most boys these days begin puberty between the age nine and 14 but some begin as early as eight years. Apart from the scrotum elongating, the testes growing bigger, getting taller and bigger, breaking of the voice one will develop beards, axillary and pubic hair during puberty.
Puberty also is accompanied by development of apocrine or scent glands in the armpits and anogenital area. Our bodies produce two kinds of sweat: one from the ordinary sweat glands, (for temperature regulation) and the other fatty one from the scent glands.
Both sweats actually, have no odour. Scent glands sweat is
responsible for the yellow we find on white wear rubbing armpit areas and pants. The apocrine sweat is also broken down by skin bacteria leading to the body odour of adolescence (kavubuka/ekikara). When at school the boy plays and sweats more apart from wearing his uniform longer resulting in him coming home with a smelly shirt and probably pants that you do not smell.
The odour being usual and normal does not require eliminating but may be reduced by good body hygiene (bathing with soap at least twice a day and drying the skin properly) and washing (using odour-fighting detergent such as Tide), ironing and changing his clothes often.
If you must eliminate the odour, you require eliminating causative bacteria by applying diluted Hydrogen Peroxide in the boy’s armpits and groins in addition to good hygiene.
If the boy sweats excessively he can use an antiperspirant/deodorant containing aluminium chloride apart from using a deodorant.