Great buck! If you still have the lower jaw you should send a tooth in to be accurately aged. I have been doing this with all my mature bucks the last few years and am sometimes amazed at the actual age of these animals. I've had some "experts" look at my deer and be off by more than a few years.
It is truly interesting how deer wear teeth differently.
A buddy killed a really good buck that looked like 3yr teeth wear and he sent tooth out and it came in at 5yr.
Also had a buck that we swore was 6yrs+ based off the tooth wear...he had 6" bases and scored around 140" as a 9pt weighed 195lbs middle of the rut...and it was a 3yr old.
I shot a 4yr old buck that only had 4" bases but lots of length 151" deer. Looking at his mass you would have thought i messed up and shot a 3yr old but i knew the deer and had pics from the previous two years.
It depends on the individual animal and the food sources they have available...or how much they chew their cud. If an animal has access to mineral licks or spends a lot of time breaking down rough browse it will wear the teeth out quicker than a deer that spends its time eating soft grasses or grain.
Only way to really know a deer age is either tooth cut age or a picture history of the buck...helps to have an identifying characteristic like cut ear, facial scar, puffy knee joint, old wound etc.
You can tell if a deer is 4yrs old quite often by bone structure...shoulders...hips and facial features...BUT this is only going to give you 4+ on age at skeletal maturity. There are some 3yr olds that can be bigger deer. Just like people...you can have a 6ft dude that weighs 150lbs and a 5'8" dude that weighs 300lbs...
You can guess the age of a deer by picture correctly 80% of the time...and dentine wear probably 90% of the time but there are always the outliers that are the exception to the rule.