I grew up cooking for large groups.
My mother died when I was 13 years old. I was the oldest of 5 kids, and my father decided that cooking was 'women's work'. At 13, I was the closest thing to a woman in the house. He was also fighting a lot of family members that were telling him that he couldn't raise 5 young children on his own. He decided to 'show' them, and invited both sides of the family for Thanksgiving dinner at our house. Guess what - that meant I had to cook it! However, Mom died in April, my birthday was in June, and Thanksgiving is in November. I was no longer 13 - by now I was all of 14!
I had never cooked a turkey in my life - or the rest of the stuff that was expected to accompany it. I got up early and spent the entire morning on the phone with Grandma, as she talked me through the process of cleaning, prepping, stuffing, and roasting the birds (yes, that's plural - 2 25+ pound birds). I literally did it on the phone with her all morning. I made all the traditional sides (traditional if you're Irish), mashed potatoes, yellow turnips (rutabagas), parsnips, Brussels sprouts, cranberry (this was canned), dressing, etc. Other than the cranberry, it was all from scratch.
Yes - I really made my first big dinner without a cookbook or a recipe or a mother - it was all done on the phone with Grandma throughout the whole process.
Mom was one of 5 kids, and Dad was one of 4. They all had husbands, wives & kids (lots of kids - we're Catholic). And most of them came to see just what a disaster Mike (my dad) would make of this.
Someone had to pick up Grandma because she didn't drive (she was born in 1890, European women didn't drive back then), and she brought the pies (Thank the Lord).
At 14, I made my first dinner for 30-40 people (minus the desert), and I've never looked back.
After that, my aunt, my grandma, and I went into rotation for the holidays. Eventually (as an adult) I inherited all holiday cooking.
Now that I live in Florida, many of my friends have retired down here, and have no nearby family. No one asks, they just expect to show up here on holidays. Some are widdowed. Some are lonely. Some are gay. Some have children who are estranged. Some only see their kids once a year. But I have holidays for everyone who needs a family. It might be 20 people or it might be 40. Christmas, Easter, Thanksgiving - everyone shows up. The same thing goes for birthdays - I may have 10, or I may have 40. But I am everybody's Sister/Mother/Daughter and I make sure they all have birthday parties when their families are up north and can't be here.
For me, dinner for 10, 20, 30, 40 is just what I do.