When you’re thinking about adopting a dog from a rescue, don’t overlook older dogs. They make great pets for a number of reasons.

1. The first, and probably most important reason to consider bringing an older dog into your life? You’ll be providing a home for a dog with life experience that—by virtue of his seniority—deserves a loving, caring home. These dogs are ready to give love by the bucket-full and to be your instant companion.
2. Older dogs are almost always housebroken and don’t require the commitment of time and dedication needed to teach a puppy the rules of bathroom etiquette, not to mention time spent cleaning up little “surprises!”
3. Older dogs are fully-grown and mature; so you know exactly what type of dog you’re getting in terms of size and temperament, rather than guessing with a puppy.
4. Older really IS wiser, in many cases! Older obedient dogs are generally more patient, less rambunctious, and more disciplined than puppies.
5. Since the majority of older dogs are housetrained, obedience-trained and probably know several tricks, demands on your time are significantly less than puppies or younger dogs; which leaves more time for yourself.
6. Older dogs are used to normal everyday schedules, increasing your chances of getting a good night’s sleep, because they sleep when you do. Bathroom breaks, feedings and playtime are reserved for daytime.
7. No gnaws, nips or bites! Older dogs have already gone through the teething phase, sparing your dining room furniture and best pair of shoes from chew marks.
8. Older dogs can often be trusted for longer periods alone than younger dogs (of course, you should never leave him alone for longer than entirely necessary).
9. A trained older dog will know many more commands, and have a greater attention span, than a bouncy pup.
10. Older dogs may have lived through the death of a previous owner, or abandonment by a less caring household than yours; this often makes for a very loyal, grateful companion!

Source: 10 Great Reasons to Adopt an Older Dog