It depends on his attitude and your local weather. It's best to limit trips in cool weather, mid 70+ is a good temp, the cooler the weather the shorter the trip unless you bring heat.
Some dragons are terrified of the outdoors, so you'll want to make sure he feels ok out of the house and won't bolt away. Spend some time out I the yard or porch or whatever you have so he can get used to the noises and sights before trying any trips.
We've been traveling with Pepper since he was about 5-7 months. He is particularly mellow though, and never tries to run/jump away. We don't really take him to shops (I'm worried about the commotion stressing him and him potentially getting sick) but we've gone to the park and spend a lot of time in the yard in the summer.