I'm running out so first things first, it doesn't have to be a shounen-ai manga, it can be like a shounen manga with a gay couple in it or any other genre. Specifically, I'm looking for at least one of the guys to be in his 40s or older, the age of his partner isn't important, they can be the same age or have a huge age difference. I have a preference for if they have wrinkles but it's not a requirement.

Thank you in advance

The obvious mention is probably Naono Boura. Many of her stories contain a character described as "middle-aged":

Hada no Ue no Renai Jijou
Harem Days
Renai Nenrei, and
Yuuwaku Sentiment, to name a few.

Most of Nishida Higashi's works also contain older characters (without as large an age gap).

Some other titles:
Sumanai!! Masumi-kun by Itsuki Kaname
The Rain in Montecarlo by Kumota Haruko
Lies are a Gentleman's Manners by Matsuo Marta (If Paul doesn't meet the age criteria, then his older brother should.)

You can also try browsing the list of series tagged 'Oyaji Romance' (here and here).

I hear Naono Bohra specialises in BL with older MC's, though I haven't read any of her works.
Sumanai!! Masumi-kun
Kinou Nani Tabeta? is seinen so it's not a romance, just a slice-of-life with a M/M couple, one in his early 40s and the other late 30s, I think.
Polaris Bell
Amato Amaro and all its associated series.
Inu mo Kuwanai, maybe. I haven't read it yet, so no guarantees.
Koh-Boku

There are a lot of searches you can use, too. Try combining the Oyaji Romance, Older Protagonist, Older Male Lead, Older Lover, Old Man category tags with the yaoi and shounen-ai genre tags. That should turn up a good number of titles, since tagging for BL is very enthusiastic here on MU.

I've read all Naono Bohra's stuff, read Hada no Ue no Renai Jijou, harem days,Renai Nenrei, Yuuwaku Sentiment, Sumanai!! Masumi-kun, Amato Amaro, and Koh-Boku.

It is worth pointing out the reason I ask, is that I've read everything in the oyaji romance section and am looking for stuff that was missed, or has a minor role in the story.

Thank you though for the couple that were suggested.