Turbo Trainer Advice

Posting this in the hope it might shame me into riding more.

1-10 mins - around 85% mhr
10-17 mins - around 90% mhr
17-20 mins - between 93-95% mhr

Average power - 300w :-(

How often would you suggest I do such a test? I have no specific goals other than trying to defy the ageing process get fitter on the bike.

I was thinking of doing this test every 3-4weeks. Too often? Not often enough?

Once a month is enough for fitness testing. I usually do 3 weeks build, 1 week recovery (lighter) and then you would do the test.