This is an interesting way of reflecting on one's life.

I have calculated my ROL (Rest.Of.Life i.e. before been garbage collected) productive hours (hours dedicated to side projects) in a similar way, and the result panics me.

Assume that I still have 37 years before been garbage collected, and 35 years before cognitive degeneration:

Starting from today:

[Time-frame 1]:

I have 200 days before kid goes to primary school. That's roughly 56 days of weekends and 144 days of workdays. For each weekend day, I'd assume an average of 2.5 hours of productivity towards my side projects (I do have more but some are dedicated to gaming and light reading). For each workday, I'd assume an average of 1 hour (usually it is a burst of 2-3 hours for 2-3 days followed by 0 hours for 3-4 days). So this gives me 562.5 + 1441 = 284 hours.

I think this is a generous estimation because I'm struggling with minor depression from time to time, and TBH I hate my work, so I lose a day if either flares up.

[Time-frame 2]:

Kid is going to spend roughly 6 years in primary school. He is going to get friends and gradually gives me more time if he chooses so. However, I'll probably spend more time checking his assignments, talking to him, and introducing him to some hobbies in hope he can find his passion as early as possible. I read "iWoz" and would like to influence my kid as his father influenced him. The upside is -- I can work on my hobby while educating him by just doing it. Downside of primary years is that he is going to weekend classes and clubs so those will take away my time too.

I'd give myself the same 2 hours every weekend day, and 1.5 hours every working day. Let's take 250 working days and 115 non-working days (weekends + holidays). This gives 2501.5 + 1152 = 605 hours each year, and 3,630 hours for 6 years.

[Time-frame 3]:

Kid is going to spend 5 years in secondary school. Judging from my own experience, he is going to gradually leave his parents alone, rebel against them, and stay much more time with their friends. I don't really know about my employment at the time, but let's assume I'm still working a corporation cog.

I'd give myself 3.5 hours every weekend day, and the same 1.5 hours every working day. This gives 2501.5 + 1153.5 = 777.5 hours per year, and 3880 (rounded down) hours for 5 years.

[Time-frame 4]:

Kid is either going to a college or a technical school. Either way, we will probably rent him a condo close to where he studies. I'll also probably go into consulting if possible, or at least take some long breaks during this time frame. If I want to learn General Relativity, this is probably the last chance. I don't think I'm as lucky as those who still possesses a sharp mind in their 70s, so 10 years between 50s and 60s is my best shot.

I'd give myself 5 hours every weekend day, and maybe 2.5 hours every working day. This gives 2502.5 + 1155 = 1,300 hours per year. But I'd be in my mid-50s so this is probably an overestimate. I'll round it down aggressively to 1,000 hours. I can keep the same schedule for 5 years, so 5,000 hours for 5 years.

[Time-frame 5]:

I'm not sure what my cognitive ability looks like in my 60s. I'll have a lot of time, like, 10 hours every day because I don't want to work after 60. So that gives me 3,650 hours per year, and 36,500 until I'm 70, at which point I believe I wouldn't be able to pursuit serious academic or technical objectives. I know, I know, many people can still do it, but I don't think I can do it. I doubt I can work on side projects more than 5 hours per day, so I need to cut down that number at least half, to 18,000 hours. Probably more TBH.

[Time-frame 6]:

70 till garbage collected. It's going to be mostly volunteering work or looking after grandchildren or travelling with my wife, so 0 hour.

[Conclusion]:

Overall, if my mental health and physical health is good enough, my calculation is that I can put 30,000 hours into my side projects. That is, I have to be very lucky to get this number. No mental issues, no heart issues, kid doesn't cause any issues, wife is healthy, etc. In reality, probably a half or two thirds are more realistic.

Isn't that scary? There is so much to learn, yet so little time.