Old Dogs is a great movie to see if you're looking for some casual entertainment. I'd recommend it for date night and/or for family night. It's the kind of movie that is best enjoyed if you can suspend disbelief and just go with it. It's better if you don't question things like the short-notice ability of two 50+ year old single businessmen to come up with scouting outfits for themselves and their young charges (who come to visit with only one small suitcase apiece).
John Travolta and Robin Williams seem to enjoy themselves in their roles - business partners who are suddenly responsible for a pair of 7 year old twins. These two belie the adage that you can't teach old dogs new tricks. Both experience significant personal growth during the month of their lives the movie covers.
For the most part the comedy is low brow, with the usual fare of farts and groin-racking incidents. There are plenty of pratfalls, which will make you wince if you're over 40. I believe Robin when he complains that he has bad knees.
John and Robin are repeatedly mistaken for the twin's grandparents and are also repeatedly mistaken as being a couple (such as when Robin introduces John as "his partner" - the natural assumption is personalpartners rather than professional). Fortunately, they're able to take all of this in stride with self-deprecating good humor.
I would have preferred the movie not waste time on offshoot tales, such as spray-tans gone wrong (Robin in a tanning booth getting over-done while John is hitting on the negligent attendant) or other irrelevant side stories (a tattoo that requires the shaving of Robin's chest hair) to allow for more character development. The romance between Robin and the twins' mother "Vicki" might have been more believable if we'd been allowed more opportunity to understand her motives and interests.
Some of the humor might have been a little over-the-top, but many scenes had the entire theater heartily laughing. It was nice to see Robin and John poke a little fun at themselves and each other; that certainly added to my enjoyment of the movie. I'm really glad they didn't try to ignore the very real age gap. Robin and John's chagrin at being mistaken as grandparents may have humored me even more because I'm a grandparent.
If you're looking for a movie that is lighthearted, relatively inoffensive and effectively mindless in its storyline and humor, I recommend Old Dogs. It's not meant to be an intellectual movie; it's simply a fun opportunity to share some laughs.