It's not possible. Teen and adult clothes are different in size, and will need different meshes. There will be huge neck gaps, animation troubles, and other size related mess.
You can only gender convert clothes safely between child male/female, toddler male/female, and age convert between same gender adult/YA/elder through SimPE without getting these problems. These three share the same size and skeleton. Adult clothing converted to elders will not have slumped and saggy bodies like other elder clothing, but will use the normal adult body. Same goes with elder to adult, where the adults will have the elder body. Young adults share bodyshape with adults, and those two are usually 100% safe to age convert between themselves, without no troubles.
In rare cases you can convert from one gener to another of the same age without getting troubles, but normally this will cause neck gaps you'll have to fix through the mesh.
With the
Wardrobe wrangler you can easily gender-convert toddler and child clothing, or age convert A/YA/E clothes. Just a couple of button clicks, and you're done. For everything else you'll most likely need to learn some meshing.
There are tutorials on how to age convert meshes (and gender convert in the correct way). If I manage to locate the one I've recently used (and found very good), I'll post a link.
And the WCIF section is the wrong place for questions about creating, so I've moved it for you.
