This is a very interesting topic. I haven't heard of a GM, that started in their late twenties. But I have heard about one person, that became an IM at a late age, and he would have been quite popular. But, to quote Garry Kasparov: "Hardworking or Talent. Hardworking is a Talent itself", I think that you've got to want to succeed and have to study hard, to become a GM, after all, as a GM, at least it seems so to me, you need to have solid and ever expanding Openings, you have to memorize games by heart, have to know most endgames and middlegame-strategies and the list goes on and on. And so it seems possible, that even an elder can become GM with enough dedication, training, meorization, the ability to quickly adapt and calculate as well as practical knowledge. That said, I don't know about any one who started late and still succeeded. But is it possible? Probably! Is it likely? No, it ain't! But this is entirely speculating, so, who knows? Maybe there is a GM, that started very late in life, but still became a GM?
GMs/IMs who started late?

I don't I want to delude anyone into thinking they'll be the next Kasparov or anything, I'm just looking for some sources of inspiration I can refer to. Thanks for the answers so far... any others?
Yes, Fischer started late. He was 6!

Yes.
George Hastings started playing chess at around 30 or 31. Amos Burn learnt chess after retiring from business. Other names include Janis Klovans and Leonid Stein. A Yugoslav GM got his GM title at the age of 72. Alexander McDonnell began serious for chess at the age of 27, in 1825. Chigorin entered his first tournament at the age of 27. George Salwe (second highest ranked player in Poland) entered his first tournament at 42. Amos Byrne started at 38. Joseph Henry Blake peaked at 63. Bernard Friend became a master at 71 and Oscar Shapiro was 74 when he attained that level.
If anyhow this was less as an inspiration for you, read this:
https://www.chessbase.in/news/M_S_Thejkumar_shares_his_journey_to_the_top
In George Eliot's words man, "It is never too late to be what you might have been." I know my rating doesn't approve me saying all this, but this was just to push you, and me as well. Good luck :-)


Chigorin did not start playing till his mid 20s
I thought he started at age 16?
He learnt the rules when he was 16, but he did not take the game seriously until in his twenties.

Famous French artist Marcel Duchamp learned chess as a boy but only played chess casually with his siblings until he met a group of artists who played chess in Paris when was in his early 20s. He didn't get serious about the game until he fled to the USA to avoid World War I, playing at the Marshal Chess club in New York. He fled the US draft in 1918, going to Buenos Aires and deciding, at age 31, to study chess full time.
He returned to France after the war, moved to New York for a few years, and became a very strong player. He was on the Marshall Chess Club team when they had matches vs other chess clubs, finished third in the Belgian national championship, became chess champion of Paris, champion of Normandy, won an international tournament at Hyeres in 1928, played on the French Olympic team (five times) along with Alekhine, and won the European correspondence championship in 1935-39.
He moved to the US in 1942 and continued to play in tournaments throughout the northeast. The US Chess Federation introduced a rating system in 1950 (later tweaked by Arpad Elo) and Duchamp, well past his prime at age 70, achieved a 2413 rating.
FIDE didn't introduce the GM and IM titles until 1950, after Duchamp's international play was over. Not considered prominent enough to get an emeritus title as some older players did, his accomplishments, including wins vs such famous players as Znosko-Borovsky, Colle, and Koltanowski (and a draw with Frank Marshal) indicate he was IM strength.

Chigorin did not start playing till his mid 20s
I thought he started at age 16?
He learnt the rules when he was 16, but he did not take the game seriously until in his twenties.
Wouldn't he still learn before that

Simeon Furman is another example.
According to Wikipedia, he did not get the GM title until he was 46.
Want me to be to say it lol Ithink most people have the potential to be 2200+ but most people will not be 2200+
# 1 Btw would 13-15 count as starting late lol cause I don't plan on competing in otb till 20+ years old at least

wow, a 13 years old forum post that keeps on going... Whoever read the first page at the beginning should have become already a master by now... isn't it?

International Master
There are National Masters, Candidate Masters, Fide Masters, International Masters, and Grand Masters. You'll also hear of Super Grand Masters but that is an unofficial title for the best Grand Masters.

No. National Master is a title given by some countries' national associations.
The other titles are given by FIDE the international chess federation. GM > IM > FM > CM

As Lord Phan states, National Master is a local title, given by your own chess federation (ie: by the USCF) and not by FIDE.
The other titles (CM, FM, IM, GM) are all FIDE titles.
Actually Jacob Murray did start chess very late (18yo or 20yo, forgot) and did become a GM. But I haven't heard of other cases.