If you start from scratch with an edible forest garden, you need at least 6-10 years for fertile soil, healthy and stable fruit trees with good harvests and other things (regionally different, of course). But better would be 10-20 years. Be sure to check the soil in any location. With fertile soil you can save a lot of effort and time.

In the temperate zones it is cold for many months. 1 or more greenhouses are a great advantage there. I'm already older. If I could restart with a #FoodForest and #Permaculture, I would prefer a warmer area with sufficient water(!).

These are my experiences from the 'sand desert' in East Germany (Lausitz). So the best age you can calculate by yourself. Start as young as you can. :)