If you don't feel comfortable adopting the five month old, then I say adopt one of the 3/4 year olds. The 5 month old will get adopted out really fast if you didn't adopt him just because of his age. So, if you adopt one of the older ones I think you would feel really good in knowing that you really helped two boxers in rescue.
That is what I would do anyway! Good luck with your decision and let us know what you decide. :wink: