In reply to Shack.

Hi Shack....never too late to get back into theme development. To be honest though, you do not have to use a framework because you can be successful without one. I use the front-end framework Bootstrap v3, but I only use the grid structure only; you do not need to use the whole thing. You of course, also have the option to do your own responsive layout.

Regarding Theme Forest, that is of course an option for you, but you may want to consider making and providing themes on your own site too. Theme Forest reviewing is as I said, can be controversial and I estimate 1 in 10 themes submitted get approved. I would not make theme forest your primary job unless you have another source of income to depend on while you try them out.

The other option in addition to building and providing themes from your own site is to look to the themes directory at WordPress.org and .com as well (which is temporarily closed to new submissions). I've been doing this method for several years now and it's worked well after I left Theme Forest.

Start off by reviewing the newer updated theme development and theme guidelines at wordpress.org before you begin. Remember too, that just because many other theme authors, even those on Theme Forest, use frameworks and load everything in, including the kitchen sink, don't feel like you have to. One thing to create success is to come up with something new and different, yet easy for the end-user to work with.