Hi there,
I've only had my baby beardie for a few months but I had the same problem.
One thing I found to have helped is where exactly I bathed him at.
I have a small tupperware container that I use solely for baths- however, every couple of days, when I put him in the container I would give him a few treats first. Now, if I even put the container in the tank he jumps right in.
Him being comfortable in that container has really helped him warm up to
bath time. I saw improvement within a week, and now he seems to love it. Puts his head under the water and gulps, and even swims around in circles for 10 minutes at a time- never trying to escape even though he very well can if he stands up on his tail.
It may not be a commonly used practice but it worked for me so maybe give it a try!?
Good luck!