Based on our personal experiences, we feel that the following are required to travel alone:
Be reasonably fit – If you are visiting Asian countries, we generally suggest to hire a car for local and inter-city travelling, wherever available.
Labor is cheaper and easily available in most of these countries, so there will be someone to pick your luggage for you.
But, in some European countries, The USA and even Canada, you will have to carry your own luggage.
From what we gather, even in group tours, most tour operators don’t tell you, but, you have to carry your own luggage in these countries. They like, ask you to pick from the bus to reception or from reception to the elevators.
In solo travel, you will have to deal with that a bit more.
But don’t worry! We have a solution for this:
Get into shape. A great reason to start that daily exercise that you have been avoiding.

Pack less. Check this out on how to pack less

At various tourist attractions, you will need the same energy as a group tour. Although your travel company might promise you lesser waiting periods at these places, this is not entirely true.
Need to speak a little bit of English – (Since you are reading this blog, I am sure you can). This is at least required in Europe and the USA.
Even if you know some basic English, you should be fine.
At most of the tourist destinations, everyone does understand and speak basic English and as tourism grows, chances of more countries understanding it is growing.
Be a bit of mobile and internet savvy – Required for using Google Maps, emails, checking sites and other information. (Again, I am sure that you are. If not, learn. It’s quite easy and fun)

Food – Be flexible with your eating habits – If you want the same breakfasts, lunch and dinner that you have at home, sorry, then this type of travel is not for you.
You will have to be flexible on your food habits and timings of having them. Apart from sight-seeing, travelling is also about trying out food that you don’t generally have. You are missing on something major if you don’t do this. Be flexible, eat local food, you will enjoy it.
If you are a vegetarian, vegan, lactose intolerant, gluten-free , you do generally get some suitable food at most tourist places and more so if you hunt for it. We got vegetarian food in Europe too and breakfast at all the hotels have a large amount of vegetarian dishes laid out.
Kids – Kids who can take care of themselves should be OK, but, kids who need to be carried might be a problem as you have to carry them and your luggage too.
I have seen couples struggle, so be careful, especially if you have more than one kid who needs to be taken care of.
If you are travelling to Asian countries where you have hired a car, you will be fine. If not, you will be travelling by local transportation (Buses, trains, taxis etc.). You don’t want to be carrying your kids, suitcases and backpacks….not a good idea.