i agree with those that say it COULD be too much; i agree with those that say he has time and IF he is serious and works hard, he COULD do the ride

AND I believe honesty is good, and as his friend it is important to tell him your concerns about his physical condition, the demands of the ride, and how it would be best if the "two were equal" ... then, as a friend, share your experience, encourage positive behavior, and let him figure-out the rest for himself!

i learned this from dealing with my DH -- he thought that riding a bike was no big deal, got a road bike and started riding. it only took a few rides with others to realize it wasn't as easy as he thought, and that he needed to rethink what he was doing and what he could really do ... action is an amazing teacher!

so, i say, encourage your friend to get a bike, help him get a bike, share your experience with him, say nothing else, and then let him ride ... you just NEVER know what can happen ... June is not tomorrow; June is the future, and the future is always an interesting uncertainty.