His definition is not invalidated by making money so long as the money you make is not the reason you are doing the activity.
The deadline part is a more onerous constraint but still I like his definition better than yours because of the hobbies that have negative consequences (like the mountaineering).
I think the best definition would be a modification of "A true hobby is something that you don't do for money and that has no deadlines attached." but instead of saying what it isn't (deadlines, money) say what it is:
A true hobby is a personal activity that has sentimental value.
The meaning of 'personal' here is that it would be detrimental for the activity to be attached to the world (through things like deadlines or money) and it has sentimental value i.e. it is not a chore but is actually enjoyable.
Another observation is that you sometimes want to share personal things with others but only if they belong to the group you trust with this particular secret. Hobbies can therefore have attachments but only to the world of that hobby (some niche community probably). This world can then become a gateway to the real world again since if you rise in the ranks of this community you become a part of the leadership that straddles the border between the community and the real world, the members of the community will often pay for this 'protection' - as an example, pro gamers legitimize the hobby of gaming since it becomes a possibility, however unlikely, to make a living playing games. This protection allows hobbyists to fully engage in their activity without concern for reality, hiding behind the delusion of one day becoming pro or in other cases staying relatively anonymous or legitimate due to the more extreme people taking the spotlight. For those who stand the vanguard it is a cutthroat life very much attached to the real world (deadlines, money, training, hard work) the hobby has therefore ceased to be a hobby and has become a job or lifestyle.
The deadline part is a more onerous constraint but still I like his definition better than yours because of the hobbies that have negative consequences (like the mountaineering).
I think the best definition would be a modification of "A true hobby is something that you don't do for money and that has no deadlines attached." but instead of saying what it isn't (deadlines, money) say what it is:
A true hobby is a personal activity that has sentimental value.
The meaning of 'personal' here is that it would be detrimental for the activity to be attached to the world (through things like deadlines or money) and it has sentimental value i.e. it is not a chore but is actually enjoyable.
Another observation is that you sometimes want to share personal things with others but only if they belong to the group you trust with this particular secret. Hobbies can therefore have attachments but only to the world of that hobby (some niche community probably). This world can then become a gateway to the real world again since if you rise in the ranks of this community you become a part of the leadership that straddles the border between the community and the real world, the members of the community will often pay for this 'protection' - as an example, pro gamers legitimize the hobby of gaming since it becomes a possibility, however unlikely, to make a living playing games. This protection allows hobbyists to fully engage in their activity without concern for reality, hiding behind the delusion of one day becoming pro or in other cases staying relatively anonymous or legitimate due to the more extreme people taking the spotlight. For those who stand the vanguard it is a cutthroat life very much attached to the real world (deadlines, money, training, hard work) the hobby has therefore ceased to be a hobby and has become a job or lifestyle.