QuestionAt what temperature is it too cold for 20-30 minute walk for my 4 1/2 month boxer male?
AnswerFirst, Boxers are short-haired and cannot remain warm as a long-haired dog. They have no protection.
Secondly, they are short-nosed and cannot take heat; no more than in the 70's. So, they need controlled temperatures in the 72-78 degree range at all times.
They are not outside dogs, especially in cold climates such as yours.
If you insist on walking him in the winter when cold, put a coat or sweater (preferably a winter coat made for his size), and walk him no more than 10-15 minutes. Allow him to wear the coat once inside the house for 3 minutes before removing it so he can adjust his body temp gradually.
He is still a baby, and cannot bear cold temperatures. No Boxer can.
The German Shepard, Husky, Retriever, etc., can bear colder temperatures.