Hi.
I have to say, right around your age, or maybe a year or two after, I began to feel the same (I'm 34 now).
I'm in a very different life circumstance than it seems like you are - I am Single income, low income, no kids, rent, have a cool dog, no real estate.
I can't say finding out about FI or mustachianism etc. "helped" this feeling... because I was already beginning to struggle with doing anything outside of the mundane/ things that make me money...but THEN I discovered that I maybe should start saving even more money... so I cut out a LOT, and it sent me kind of spiraling into deprivation, where I somewhat live now. I'm sort of making my way out of it... but I do want to say that I empathize.
It can all seem sort of gray, repetitive, and pointless sometimes, right?
FIRST, with all of that being said, I'd like to say that it is ok to consider going to therapy.
Therapy is NOT just for when your life is in a full on crisis. Therapy is not just for when you need help picking up the pieces of your dreams or psyche, or... whatever.
Therapy can be great for offering some support in moving through the slightly sticky spots of life.
And if you have the financial means to go to therapy, OH MY GOD GO.
I would have LOVED to have been in the financial place to have gone to therapy when I started to have similar feelings.
Ok, also....
I have found that being involved in community activities has given me a WICKED STRONG sense of purpose. I try to automate as much of the mundane as physically and financially possible so that I can be involved in some type of community activity.
And I get the sense that you are a PLANNER. So plan that shit.
Example: On Wednesday morning you to to a community workout, on Friday you and your wife play on a rec kickball team that always goes to a different brewery after. Maybe the dues are $20/mo and you each get a beer every week. So $60/mo... and if you can afford to automate whatever else would have been happening during that time, add that price in too. Ok, can you afford $100-$150/mo to make sure that your life feels meaningful? If you CAN afford it, but are hesitant... you are devaluing your happiness (and jump to the therapy suggestion above).
There are lots of choices depending on your interests and budget:
Gardening Club
Club Volleyball
Second Language classes
Kickball Clubs
Running Clubs
The November Project/Seal Team/ other outdoor workout activities done in GROUPS
Crossfit
Cycling Meet ups
Dinner Clubs
Craft Meet ups
Hobby Woodworking Groups
Yoga
Barbell Club
Swim Club
.... Yes, it's going to be REALLY AWKWARD the first time that you go... Maybe even the first 11 times (or 789 times) that you go... Maybe you'll never feel super comfortable, but I really do advocate for community time. You mentioned your work, your investment property, and your wife... but nothing else in terms of community, and that REALLY makes a huge difference. I'm agnostic, but I've even considered going to a Unitarian Church for the community aspect. So church could be a choice too, if you wanted to.
Consider combining some of your activities. Are you wearing a weighted vest while you're mowing the lawn? No? So cut back some of your steady state cardio and now the lawn mowing (if it's push mowing... please don't wear a weighted vest if it's a riding lawnmower- ha)... boom, ok that's ten minutes off of each workout each week. Sneak some other bodyweight workout stuff into your work day, or during chores. Ok cool, so now all that's left is weightlifting... maybe you can join a barbell club, as mentioned above? I'm guilty of over-optimizing, but I do really love when I can combine required activities to open up time for something more preferred. Try it! :)
I've also found, through time in the fitness world, that there are a LOT of "programs" for adults to learn to have fun again... and it's suuuuuuch an interesting concept to me (nothing I would ever try though). If you're not familiar with Ido Portal, maybe you'd be interested in his stuff, or Move Nat or Animal Movement or something like that. He's very much not my cup of tea (I think I kind of hate fun, or forget how to do it... again, I am in the same boat as you so I am as much here with suggestions as I am to follow the thread)... but a lot of people really love him/ similar programs..
Also, I'd like to say that maybe you should ignore the suggestions that you should have a kid. In my opinion, you shouldn't have a child because you feel dissatisfied or sad about life... you should have a kid IF you want to bring a human into the world. Kids are not band aids for pain.
Just my two cents. :)
Good luck.
Hoping to follow along too!