If they don’t ask beforehand, the first time you get whiff of the BO, it’s time to start having a talk with them about hygiene and how to look after themselves.
I would start with a natural deoderant, one free from aluminium and desiged for sensitive skin. But you could take them with you and let them pick out a scent they like.

At that age they certainly can start getting smelly and a natural deodorant can be approproate

My daughter started around 10 – i found this product called no pong that works great for us.

I know a few that started at 11, 10 and 12. each child was different in their activity.

With nine year olds it’s more likely something they’ve rolled in, stepped in, or touched! I gave my kids deodorant at around 12 years, but my daughter got some at 10 years because she wanted to be like her siblings. Didn’t really need it, though.

Yes it would not hurt to give him some now but not the Aerosol ones roll on only

i think my kids started wearing it in abut grade 5 or 6. I think it depends on the kids but I think once the smell starts its time.

Was probably high school- 15 when I started!

I would buy it and show him how to use it.

Our kids are very young still but I remember buying deodorant packs for my nephew when he was around 13/14. He was already using though a few years prior to this. His parents purchased for him and it was discussed the use of deodorant and then given the choice to wear.

Maybe get them involved in choosing a deodorant they like too.

If he’s smelly I’d be doing it now. Make sure he is washing himself thoroughly though, he may be just standing in the shower.

I remember using deodorant for the first time in year 6. I think my mum was trying to prepare me for high school lol.

Deodorant is good when they start to ask for it or it is discussed. Being active in sports etc we started to use it pretty early on for all.

It can come down a lot to diet. Trying to drink more water to flush toxins out, more wholefoods and less processed foods can make a huge difference if they have been eating lots of processed stuff lately. I myself used deodorant for many years, before realising and understanding the dangers of using products with aluminum in them, especially on the underarms. I switched to a natural deodorant and used that for about a year while changing my diet (less alcohol, sodas, processed foods like lollies, chips, processed meats) and I realised in that time I actually stopped needing to use it. Have not used deodorant in about 5 years now. If you think they need it right now I think it’s fine for them to start using it just try to find something without aluminum.

As soon is you start to smell them 🙂
Kids start to have body odor around the time puberty starts and hormones change. Usually, this happens when females are 8–13 years old, and males are 9–14. But it can also be normal to start puberty earlier or later. Bathing every day, especially after a lot of sweating or in hot weather, can help with body odor too of course