As long as you can ensure that they don't escape, you can, and should, take them out frequently at every age. The sun is the best source of UVB around, and spending time outside is very good for them. My Xander is about 7 in. SVL and he spends 30-60 min. outside everyday. We use a hip harness for him, and he does very well with it. If you have trouble putting it on, maybe you could get someone to help you? I've found that I can get Xander's on alright, but I have a heck of a time getting it off.
If your ig has trouble with a hip harness - if he pulls against it or croc rolls a lot, you might want to tame him a bit more, since they can still get hurt even in a hip harness. You can build an outdoor cage for him to get him some sunlight if the hip harness isn't working out. Just make sure that the wiring you use is nice and wide so that the UVB can get through - and never put him out in a glass container.
And don't forget to keep an eye on the temperature. You don't want him to get too hot or too cold. Be ready to mist him and provide some shade and bring him back indoors when necessary.
There's some good reading about this on iguanaden.com. Look for the section called "the great outdoors".
Alika