I am 45 years old Danish guy and have to date had the good fortune of travelling to 170 of the worlds 193 UN-countries (so I cannot answer the question fully but I am on my way). I have a full-time 9-5 job (IT Sales), a house, a girlfriend and two lovely children (born in 2006 and 2009 who have by now visited 68 and 52 UN-countries).
So how can you do the same?
1. Money. Prioritize spending money on travel over everything else. It's basic. If you are not loaded then save every penny. You already know how. Go to H&M not Armani. Don't smoke. Don't go to fancy restaurants too often. Take bike/bus not taxi. Buy your furniture in Ikea. Go for a small house/flat and an affordable used car. Don't get a new kitchen.
A Danish friend of mine has been to 100+ countries while being a single mum and working as a daycare mother. And another friend has been to a 150+ countries between working simple jobs and being on welfare. It can be done if you want it bad enough.
My budget for every country in the world is GBP 125.000. Over 25 years that is 5.000 GBP pr year (625 GBP pr country). If you can save that amount you could do the same.
2. Time. Travel every time you have vacation - try to get a few extra weeks of holiday (self paid). Travel for longer periods between jobs (I did 2 x 1 year solo and 8 months with my girlfriend). Use every possibility of leave from work. We took our kids 3 months around the world on maternity/paternity leave.
3. Research. Book everything yourself. Stay in local guesthouses / Airbnb / couchsurfing - it is cheaper and more fun. Search for cheap flights. Use local transport often, or get a cheap rental car (no matter how small as long as it can drive). Buy open jaw flight tickets (or two single tickets) and travel to a region flying in to one capital, take local buses/train and fly out of another. I have done this numerous times (check here for my maps of multi-country trips): A 4-week holiday for two adults and two children in 3-5 countries can be done in the cheapest regions (like Eastern Europe where to flights are cheap) with all expenses from GBP 1.800 (total for 4 people) ie.same price as some people spend on a one-week family charter holiday. Research and planning is hard work (especially when getting visas to difficult countries) but it is absolutely essential and the key to successful independent and cheap travel.
Mountains near Bokonbaevo, Kyrgyzstan
4. Have no fear. The world is not dangerous. People are kind and friendly. Start with easy countries. Build it up from there. I would have never believed if anyone had told a younger version of myself that I would one day bring my young children to some of the "world’s most dangerous countries". Now I believe that with the right amount of planning and precaution you can take your kids anywhere.
Unawatuna, Sri Lanka
5. Travelling with Children. Just bring them. Kids love exploring. Kids are highly adaptable. Kids open doors. Kids are curious. Kids are happy when their parents are happy - so if you feel good travelling with them odds are they will feel the same. Maybe your kids are different - mine are happy wherever I bring them.
See more of Jakob's adventures on www.expedition-everywhere.com.