For both my kids, the first six - nine months were rough since their sleep patterns aren't established and if I don't get a decent night's sleep I feel terrible the whole next day. Pile day after day on that it really wore me down. So I'll say anytime after the first year is great. When my son turned 8 and really started to 'get it' about stuff we were able to bond much better. It's like a switch flipped and he started to understand jokes and how to tell them, he could sit and watch a baseball game or football game and understand what was going on. He read a book for the enjoyment of it. This may be a silly dad thing, but he was playing 2nd base and caught a pop fly and just flipped it to the shortstop for the double play. That was incredible. Before that, he could have caught the ball but wouldn't do anything about it, but he did it really without thinking.
The majority of kids are fun to be with if you respect them as individuals and let that individuality come through. When I was working at children's centres those children who were, shall we say, not always likeable most often had messed up home lives. Most kids are remarkably resilient, but they still need respect and clear guidance.
) We stayed up until 1 AM last night having a blast talking with our 18-year-old daughter who just finished her freshman year at Yale. She's bubbling over with plans and ideas for her next school year, and the rest of her life. It's really fun to see her becoming such a creative, self-confident adult. 
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