I am learning for the first time at the age of 46, and no I don't have any ambitions to become good as it's basically just for fun. However, one thing I have noticed is that being older it is much harder to think fast and calculate fast. This means that I notice quite a lot of improvement in my correspondence chess games but I am still very weak OTB (lots of miscalculations) and hopeless at blitz (way too fast). This suits me fine as I don't have time to play OTB games anyway at the moment and I find CC really fun. My dad became a CC IM in his 50's (back in the 90s) and I find that interesting because that would also seem to suggest that you can become a strong player as an adult when time and mental agility are taken out of the equation. However, my Dad did play chess all his life as far as I know, so it's a slightly different situation from yours.
Anybody here learn chess at the age of 21 or older?

Now, at forty-eight, I train like a demon, and am rapidly improving beyond what I could expect from the foundation I laid in my youth, though that experience helps.
Great share and i admire your spirit........but this intrigue me whats motivates you to train intensively at the age of 48? I mean, dont this enormous effort in chess would distract your focus on ur present career? Lets say you are accountant now (or could be anything).........dont u think its better to increase your competence in accounting field or pursue professional certification rather than sacrifice your time for chess? I mean, lets say you finally achieved your goal to be a chess master, but so far i know, its so hard to earn money purely from chess if our rating is still below 2600. So what you get if you achieve your target probably is a personal satisfaction, but if it is the case, its also a great motive.
For harter, i think we can still train our speed with a correct method of training. Or simply avoid blitz chess and just focus on standard chess if we think we perform better at longer time control. I believe if you buy several tactic books for intermediate players such as Polgar books, you can improve a lot. No matter how old we start, i believe we can reach a rating around 1700 or 1800 with moderate training.

I learned as a kid in NYC, played recreationally against other decent recreational players, but with very little theory until I turned seventeen and spent a summer in Washignton Square Park playing Richard Gilmartin two hours every morning, then applying his lessons in the afternoon against my peer group.
From age twenty to twenty-four, I trained fulltime (70-80 hours a week), but quit in 1991, playing intermittenly. Now, at forty-eight, I train like a demon, and am rapidly improving beyond what I could expect from the foundation I laid in my youth, though that experience helps.
Can it be done? Yes. If you get past why a player with the necessary talent didn't bother doing it before, or that a player who tries to become a champion at 30 against 2015 competition didn't try it at 20 against 2005's best, etc. For as great as Kasparov may have been, winning the world title in 1985 from Karpov didn't take that much compared to beating Carlsen today.
If a child can go from birth to GM in ten years, I would think an adult could do it quicker.
I noticed your book description on Amazon states:
"Former USCF EXPERT Ray ("Mr. Miniature") Gordon"
What name is your USCF rating under? The only Ray Gordon I can find is rated WELL below expert and has only played 4 games, the last being in 2005.
Was perhaps going to buy your book but without any kind of verification of your rating I will not.
Also, what do you consider "rapidly improving beyond what I could expect from the foundation I laid in my youth"? What kind of numbers are you currently experiencing and how are you measuring it? What chess federation are you playing in to get a rating currently?
I learned chess at the age of 23 (more than 10 years ago); and since then i have played chess on and off, mostly just for fun or killing time. I never studied chess seriously, except try to solve some tactic problems (but do it occasionally, not a regular training).
Has anybody else started to learn chess at adult age? If yes, have u still had any chess ambitions such as reach a particular rating or immerse yourself in a special regular training? For me, the pressure as an adult push me to focus on my career and abandon serious chess. But its still great to hear someone experience to pursue their chess dreams at an "old" age. Well, lets define "old" here if you just learned chess at the age above 21.
Since many believe that learn chess at 21 or older is already too late for a chess career, so whats drive you to set a specific target achievement? Is it just for your personal satisfaction, if lets say you can reach a rating of 1800? Share your story here and whats drive your motivation?