Learning is a continuous process. There is no limit to learning, nor there is an age restriction for learning. You can learn as long as you wish to learn.

Indeed. The day you learn nothing you are either dead or practically dead.

The only age-learning cutoff of which I am aware is about age 3 for learning language. Almost every field of study requires math, so study math through integral and differential calculus, to get the basics. Additional math may be necessary, depending on the other things you study. I also recommend one philosophy class and a logic class. Then study what you wish.

The only age-learning cutoff of which I am aware is about age 3 for learning language.

 

What cut-off do you mean? Even when talking about mostly passive accent-free language acquisition it is usually closer to 5 or 6 years (and even then it depends quite a bit). And of course many learn languages successfully far later in life (though it is true that mechanisms are a different by then).

There are a variety of stages up to 5 years. See: http://www.speech-language-therapy.com/index.php?option=com_content&view=article&id=34:ages&catid=11:admin&Itemid=117

If you don't learn them as a kid it's just impossible (or nearly impossible) to learn them now.

A friend of mine had an accident with his motorbike a couple of years ago. After six months in coma he is regenerating slowly now and he has to learn everything from scratch including reading, talking, how to use his body, walking and all the things we do every minute so thoughtlessly. Just like he was reborn in an adult body together with most of his memories.

He is 36 now and if you'd ask him about your doubts of not being able to learn everything over a certain age, he'd probably just laugh.