Blue gazebo if he wants to do biology I think he should do it. I'm a biologist, never liked maths and did the minimum, it's never been an issue- I just do the maths y parts I have to, and use a calculator and double check everything.
But maybe you can leverage this a bit and say to him, it's his future and it's like training for a sport, if you want to do X, sometimes you need to do extra fitness training in something you don't enjoy as much. Opening doors, etc etc. There's no doubt maths is helpful in all sorts of parts of life.