Welcome to the forums, and God bless you in your faith journey!
Your mother is mistaken. The Catholic Church welcomes people of all ages. My wife and I were Baptized, raised, and Married in the United Methodist Church. We entered into full communion with the Catholic Church and received Confirmation together about two years ago at the age of 26.
The normal way for adults to enter the Church is through an RCIA program, which is the Rite of Christian Initiation for Adults. Normally these classes start in the fall (October-ish) and continue until the Easter Vigil in the spring. Through the program you learn about the Church, Christian history, the Sacraments, etc. It’s mostly for people who are converting, but it is also usually open to people who just want to learn about the Church.
I help with the RCIA program in my Parish, and we have had a wide variety of participants…young and old, men and women, seeking conversion and seeking information, baptized and unbaptized. All are welcome to come and learn and question and, if so called, enter into full communion.
I would urge you to contact your local Parish and inquire about their RCIA program. Also, most likely, the Priest(s) will be willing to meet with you individually to answer any questions you might have about the Church.
Becoming a Catholic has been one of the most wonderful things imaginable for my wife and me. If you have any questions about the process of entering the Church, I’m happy to answer them (here, or privately).
God bless you!