I don't know about you, OP, but I find my twists look more juvenile (read: silly) when my hair is stretched. Not only are they light (read: stiff/no movement) and wobbly and skinny, but they also look so thin and pitiful. I'll post some pics to illustrate:
Freshly done twists on braid-stretched hair on the right look so thin
These are the same twists after a wash:
Another set of freshly done twists in the top pics vs after a wash in the bottom pics:
Another example of how weird stretched twists look on me. These were straightened, and were so thin-looking that I only felt comfortable if they were flattened against my head in a way that they hid my scalp:
I think twists worn up do not look juvenile and if they are damp they can be stretched into a pony or close to one and a puff worn. When my hair couldn't make it into the puff, I just cornrowed them along where they could reach in a circular way then added a puff. That's what I did in the pic below:
This style was also created on damp twists which are easier to stretched, and I don't think it's juvenile either. So I think it's just how you style them:
OP, braiding isn't hard. Especially if it isn't for wearing out. You can learn if you really want to by practicing the rhythm on a doll. You don't have to do cornrows to stretch our twists. Single plaits can work. Braiding is simply taking three sections and then starting with one of the outside sections, cross it over the middle one. Then take the one on the other end and cross it over the section that is now in the middle. And just keep alternating like that:
How to Braid Hair | My Hair Styling Tools