Coming into season - how young?

Mya is only 5 months and Freddie my 20 month old boxer has been sniffing her lady bits all weekend and at one point tried to hump her He had his man bits out which I haven't seen since he was neutered!! He's been following her sniffing her lady bits loads too. Could she be coming into season? Any ideas?
Her lady bits aren't swollen and there's no discharge yet.

She could be near her first season, Smeags came into season at 6 months old.

I've had bitches come into season as young as 6 months old.

If you are in any doubt get her checked out by your vet.

Thanks She's fine in herself, just Freddie trying to hump her made me think she could be coming into season. I'll keep an eye on her

bitches can be attractive to dogs for six weeks or so before they actually come into season.
Dont be surpised if your neutered dog mates/ties with your bitch - but at least she wont get pregnant!

Totally agree Thandi if you could ask your breeder at what age the mother came in to season you will have a rough idea when your Mya will come in usually bitches follow their mothers cycle