Mine Ate Fruits At 3 Months And I Built One Day Entirely Of Fruits Into My Feeding Routine At 6 Months. From 3-6 Months The Protein Has To Be Offered With Fruits Since They Are Growing So Fast. Also When They Get To 6 Months Of Age One Day A Week Without Food Is Good For Them Also. Lets Their Digestion And Excretion Catch Up With Their Appetite.
People will debate this, but, I feed my veiled only dark green leafy greans such as, Collard greens, Kale, butter lettuce, etc. ... no spinich or fruit
He eats them like crazy and with these greens I am providing him with an additional source of calcium and moisture.
Concerning the age to start: I say offer them now and continue to offer them. If he isn't interested today, he will surprise you tomorrow or next week by ripping them up and devouring a really surprising portion.
The problem with trying to control when or how often is that you will at some point or another not be providing them on a day he wants them. I have experience with a veiled eating artificial plants in the enclosure. Something I am sure he would not have done if he had the real greens available. It's not expensive or difficult to add these to his routine. I would start now and wait for the fun to begin. It's amazing watching them tear the greens apart.
I have given mine greens (dandelion, kale, collards, endive, small amounts of ROMAINE lettuce, etc.) and veggies (diced sweet red pepper, diced carrot, diced sweet potato, diced squash, zucchini, etc.) and a little fruit (apple, pear, melon, berries, etc.). They also eat the pothos in their cages sometimes...especially the females.