J.B
Building Selda

Founder, operator, builder of thingsthat shouldn't exist yet.

I build companies. I started my first one at 14, scaled a marketing agency from zero to a few dozen people in 18 months, and spent the years after that pulling startups out of cash crunches, shipping products, and helping founders raise.

Now I'm building Selda, the platform for first contact that I wish I'd had in 2023.

Justus Berner
Justus BernerHelsinki · 2026
01About
A short version

I'm a 21-year-old founder from Finland. I registered my first company at 14 and started building for real at 16. A marketing agency that grew into a team of a few dozen in eighteen months.

After that I spent a couple of years inside other people's companies: turning around cash-critical situations, shaping products from scratch, assembling teams, and helping write the vision and raise the round for the next chapter.

For years I kept running into the same missing tool. A serious platform for how a company handles first contact. Nothing did it well. So we're building it. If Selda had existed in 2023, the last few years would have looked very different.

I think in long time-horizons, ship on short ones, and write down what I learn.

2025 —
Selda CEO & Co-founder
Current
2023 – 25
Early-stage operator Product, team, fundraising across 2 startups
Operator
2021 – 23
Marketing agency Founder, scaled to 20+ people in 18 months
Founder
2019
First company registered Toiminimi / sole proprietorship, age 14
Start
02Writing & Press
Selected features & interviews

A running list of published pieces about me and by me. Mostly in Finnish press, covering the early years, the agency, and the thinking behind what I'm building now.

More pieces on the way. Essays on first contact, scaling sales orgs, and what I've learned from running a team at 17. Drop me a line if you want to be notified.
03Contact
Say hello

The fastest way to reach me is email. I reply to things that are specific, thoughtful, and short.

04Last thing

If you're building something and every conversation feels like pulling a rope through a keyhole, let's talk.