You don't know, you think you know. That's a hell of a difference. Maybe you will understand it in a few years. 30 is still very young, so age is not a problem.
You basically won't get a job working for the NYSE at 31, Andy. The Wall St world is rather very systematic and traditional. -- It just doesn't hire random people like the Post Office. You need the right resume and experience and connections and abilities and etc etc. If what you meant was you want to be a trader/daytrader on your own, playing with your own account...Then of Course yes, you can do that. Most people fail or get nowhere or are simply not cut out for this type of work -- being elite is a rather very tiny club. In my opinion, if you want to be a fruitfully successful trader,...you have to be ok with basically going all in and compounding your account. And of course you need the loose general frame work all in place as well...your mind/psychology/maturity, expert understanding of what you are trading, obviously bigger gains then losses, etc etc Being a trader is tough work...the stars have to kind of almost align for you. -- it's not just like simply opening up a pizza or bakery store around the corner. Make 2018 Great Again, ET extraterrestrials...High-Five` Mazal Tov, Good Luck, and May the Farce Be With You...cock-a-doodle-do
I think you are right for the majority of people, but each trader should find out if he can do better. I needed many years to become profitable as a daytrader but if I compare my "career" as daytrader from scratch (so including the many years I did not make any money) till know with a buy and holder then the result would be as followed. Supposing I had $20,000 as starting capital. A buy and holder should make between 50-75% net average every year to catch up with me. What is easier? Daytrade or make 50-75% net every year in buy and hold? Daytrading is horribly difficult if you want to be consistently profitable, but once you found the way to profits, the rewards are exponentially bigger then buy and hold. But this is only possible for the happy few. Should he try it? Without trying he will never know. What other people can or cannot achieve will never have any impact on his performance.
This strikes me as an odd post. You seem to say that algos cut into profit margins, and then suggest the answer to this is programming your own or aspiring to being an automaton. But in reality, the HFT firms are not (in aggregate) outperforming simply holding the assets they trade frequently (remember Buffett's very he just formally won, but was long ago conceded?) Trading against algos means you're trading against the instructions someone gave to a computer previously...computers that can't say, "ok, I've hit my very precise threshold, but something looks different this time..." You're also not up against emotion (which I'm not suggesting is necessarily beneficial...I have little doubt there are profitable traders who looked for signs of panic or ecstasy), just hard rational logic. You're still watching human behavior, just a few degrees separated from the pit traders (the move from pits to screens being the first, and screens to programs being the second). You can still figure out people's intent, you just don't have the same clues. What once was screaming, sweaty, red faced, wide eyed pit traders in a panic to offload their shares became big red bars on charts. Now the goal is to figure out not when the panic sets in, but when the cold, rational, forethought says, "ok, now it's time panic." Incidentally, this rational approach to the market exposes an opportunity to predict market activity because it's already been programmed. Doing so successfully is debatable, that it can be done is not. To answer the OP, it depends on your experience and financial situation. If you've scraped together $10k working retail, at 31 trading probably isn't a natural move. If you've carefully built your nest-egg and have enough money to experiment in the market while your nest-egg stagnates for a few years, you might be able to work something out, especially if you have a financial background. Start buy leveraging your own knowledge to find what of your experience will translate well to the market, that will give you a good starting point to grow your trading knowledge.
As others have said, if you can automate your strategy, then your age won't have any factor on the system's performance. It comes down to how badly do you want to be a day trader. What are you willing to sacrifice in order to become successful? Most people in their 30s and 40s have more distractions such as kids, job, family, etc. which are usually not a factor in their 20s.
I actually argue that for you it is too early to become one if you are not one by now. The successful full time day traders I know all quit their day job to day trade because they love trading but don't need the money to put food on the table. Once fear and greed are removed from the equation, one can trade more successfully.
Where automation has really helped me is my failing ability to remember everything that is necessary, the fine details of price action breakdown, although good systems can day trade/scalp in any market in theory, it just not true, my ES systems don't work as well in Orange Juice and coffee and the systems that work in those markets well are so so in ES. Longer I continue to study and develop systems at 61yo, making systems to find human behaviors, there is just so many behaviors and most based around fear, whereas determining when and where Hedge funds and HFTs and figuring out how to beat them by nano second is today's challenges. And being on wrong side of Crude Oil when HFT comes to play, slippage of $500 has to be factored into your methods. Algos built by HFTs and hedge funds, many don't use charting, never thought of taking physics to being able to do more complicated formula's to trade, I never thought other than long term trading the I had to study more on cycles for intra trading. I think it is just much tougher to learn to day trade, and unless you one open minded person, 10k is like a down payment on the unknown. As far as predicting, we all are whether we automated or manually unless we have that smart monkey throwing darts in great Bull market, let's see how monkey picks in bear market, chances are he be in the streets dancing for a quarter. When I first started learning(I use that phase as a joke)in 1985, markets just starting to get home PC and few books that were actually decent, and now thousands of books with too much information, thousands of studies on trading software, I just believe with ALL unbelievable amounts of what is available, tougher to learn the basics and memorize all the patterns when NOT to take viable signals. Finally getting above 50s outside, so me going to enjoy weekend. Monday should be very interesting if still in shutdown.
Anyone can day trade. Last time I checked brokers will not reject your application to open an account if you are over 30.
As one gets older, his ability for dealing with account volatility is diminished (afraid of taking on risky positions, sensitive to loss. it translates to limiting his ability to make money. I think there's a reason why they tend to send young men to battle field, not old men.