I would give him a bath asap.. if you wait till he's older to give him his first bath you may have a much harder time getting him to feel comfortable having a bath. If you start it out young they will be MUCH more relaxed for future baths. Even if he's not dirty right now, I would get a mild puppy shampoo, tearless, and give him a bath just to get used to it. You might even consider taking him to the groomers instead if that's where you will be having him groomed in the future.
I agree with Binkalette. Get him a bath ASAP. At 3 months of age, he should be finished with his puppy shots and ready for a professional grooming. The younger the better to ensure happy experiences for a lifetime. A maltese is a breed that needs to be groomed regularly, and the earlier you start them, the better.
You should start a dog between 8 and 12 weeks of age.. You may not be able to bring him to a groomer just yet, but he needs to get used to a bath now....
If you wait to long, you take the risk of stressing your dog out and him being a complete and total pain to the groomer..
You should also get him in to the groomer to get used to them. You may not want a hair cut, which you don't have to do, but it would be good for them just to shave his sanitary area so he can get used to the sound of the clippers.