I almost put this one up instead of manual.A second language. or if you know two, a third.
For me, getting up there in years, I can accept loss of strength but not decreased mental capacity. Learning another language and shfting between the two supposedly works wonders developing new neural pathways. Inexpensive one-on-one lessons on italki.com, and meetup.com lets you practice with other foreign language speakers.
For AOT, it isn't too late to learn public speaking. It's simple, really. What most people need is confidence. Once you learn to project voice, pause, etc, it all comes together. Good and inexpensive courses on udemy.com. Check out Peter Baker.
Being retired in the age of the internet is awesome. So much you can learn. Last week I googled can you learn to sing in your 70's and the answer is yes, with a ton of free youtube videos.
Inexpensive fun.
Where I am from my relatives, who some did not graduate high school or graduated and stop, speak 3 to 4 languages. It is something that is natural to them but I am always floored by it.
Knowing more than one language is just good brain food, you know?