I started my first blood tracking Dachshund, Tex, in the mid 1990's at about age 3. He picked it up by the end of the the first year. So I see no reason why you could not train your 4 year old hound up. A difficulty I found was to prevent the hound from tracking "deer". I found that positive reinforcement worked great in teaching both Tex and Mojo what I wanted. Tex is gone now, at age 15. Mojo is 7 and an ace tracker. I put both on every deer blood trail that I could ... still do. No matter how short or obvious. If the hound has it in 'em, then it'll blood trail.
I am in the process of training a 3 rd. dachshund, Spotty, using deer blood that I collected last season .... and placing a treat at the end of the trail as a reward. So far so good. She has done up to about 100 yards or so of moderate blood. I hope to get her in the woods this fall with Mojo.
For "hugo27bell75ty" .... do you raise Teckel dogs? If so, I am interested in discussing purchasing a pup down the road. E-mail me.