You can major in almost anything and be a premed student. One example I saw a while back was a student who majored in art, completed the premed requirements while getting their bachelor’s degree in art, went to medical school, and became a surgeon who specializes in robot-assisted surgery. In the video they paint a very small picture of the hospital where they work using a robot-assisted surgery system. Manual dexterity seems to be a common factor.
I can think of three things that might influence a choice of major. One is to have an overlap between the classes required for the major and the classes required to complete premed requirements and apply to medical school. This might for example suggest a major in biology. A second consideration is “plan B”. What might you do if you don’t go to medical school? In many cases this might suggest “not biology” (there is often a glut of recent graduates with a biology bachelor’s degree who did not make it to medical school). Having a major that fits this plan B might turn out to be useful. Finally, what do you like and what are you good at?
It is very common for students to change their major after starting university (at least in the USA and Canada). Thus this is something that you can figure out later.
Life is not a race. There is plenty of time to get done whatever you want to get done. Graduate students are often in their 20’s, but a student in their 30’s is not unusual at all. As students mature they will often become stronger students (this applied to me for example), and will also often get a better idea of what they want to do with their life (which also applied to me).