Extra rider with plenty of energy means a lot more maintenance- so start aquiring a new tool kit- and tubes- and tyres and anything else you can afford. You know your bike will need a few upgrades so no excuses.
Be carefull on the rides you do with him. Do not attempt to keep at his speed or tackle the hills in the manner that he does. Your only saving grace is that he will not have the stamina for long rides for a while so you will still win on the riding stakes.
However--when you get to being 2nd on the rides- 60 psi in the tyres and binding brakes should slow him down a bit.
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How long was I in the army? Five foot seven.
Spike Milligan