Jimmy - I was a bit older than you at time of surgery (I was 63). The conventional "wisdom" has always been "Mechanical valves for most younger patients (except women planning on having children), tissue valves for older patients." The quandary has been the definitions of "younger" or "older."
When I had my surgery, the Cleveland Clinic (often thought of as the leader in US heart valve surgery) was using tissue valves in the majority of their patients as young as mid-50's. At that time their valve of choice was the Edwards Lifesciences 3rd-generation bovine pericardial valve. The manufacturer's tests lead them to project a useful valve lifespan of "up to 20 years." I have not yet heard of any large numbers of valve failures among that cohort - but I have had this valve for only 6 1/2years.
Given that you are "just" 50, again using the conventional wisdom, many would suggest that you opt for the mechanical valve. I do not think that you could "go wrong" in doing this. If you now opt for a tissue valve, that just about guarantees that you will need at least one re-operation. (You DO plan to live past 65-70, don't you?) Yes, you could assume that if you need a re-operation you may be able to have it done via catheter (TAVR), but so far that is just a "maybe." No guarantees. If you opt now for a mechanical valve, odds are that you will never need to have it replaced again. Yes, you would need anticoagulation therapy, but that is what you would trade for the need for another operation when you're older.
It is, as they say, "your choice." Personally, I feel that the "conventional wisdom" still holds true and that the odds are in favor of the mechanical valve patient. Bear in mind, though, that this is just an opinion. I am not a medical professional. Heck, I am not even a mechanical valve patient. Just another guy who went through the same decision process years ago.