The only person who has what it takes to tell you what is possible or not, and it stands, is still yourself. So if HE/SHE tells you can, then it is possible to achieve anything you set your mind to.
With that out of the way, the answer to this question is a resounding no. It is not too old by 38 to start a career in UX/UI; even a man in his late 60s is not too old to start anything.
Some quite inspiring people have caught attention to prove that age (whether too young or too granny) should not be a limitation as long as it’s not made one.
Kathryn Joosten decamped from nursing for an acting career, and she was near 60 when she became an award-winning rich actress.
Colonel Sanders, well over 60, was a service station chicken seller before he finally cofounded Kentucky Fried Chicken, the world’s second-largest restaurant chain after McDonald’s.
At age 95, Stan Lee was considered the godfather of Marvel Comics, whereas until later in his job, he had not created his first comic, which he made at 39.
Age is not always the best yardstick to measure anything in life.
There could be people out there who may have even started a career at teenage age, upward of 15 to 20yrs down the line, may not have recorded a break yet.
If it were too old by 38 to start a UI/UX career (in the blossoming tech industry), then it is also too old to fall in love, learn mathematics, start up a business, learn a new language, start a family, and pretty any other facet of life.
Technology does not care about age or someone’s address on the Map.
A career in UI/UX is more concerned about the technical skills you have garnered from working on real-life projects, which will enable you to land a job in the first place.
This is about the professional and soft skills developed to work collaboratively in a team, communication skills, people management skills, etc.
In the same way, the desire to get into UI/UX is not just enough. That all also boils down to what the drive is—the reason within, coupled with how bad you want this.
With the 10,000-hour rule, which suggests that you put in 10,000 hours of learning and practice to become a world-class expert in any field, it should take 3 to 4 years to get to a level of professionalism. That is anchoring on 10 hours/per day, 70 hours per week of learning and practice.
Therefore, by age 42, you should be at the peak of your career, employable at any tech company.
Fortunately, even before the expiration of 3 years of learning, one will have been a freelance developer in any of the many open gig markets, getting paid at an hourly rate while still learning.
Basically, you can see that it is neither too old nor impossible to become a UX/UI engineer at 38 years of age. It is only hard, just like other valuable things in life are.
If you can start now, invest sufficient time, give enough patience, and the practice required, you will look back to today gladly because you took that bold step!