Low max heart rate ?!?!?!

Low max heart rate ?!?!?

I'm 17 yrs old
186cm (6ft tall)
weigh 74kg (160 pounds)
I can Run 5km's (3 miles) in under 20 Minutes
I can Run 21km's (13 miles)under 1:50
I can Cycle 109km's (68 miles) in 2:45
And I can Row 2km's (1.25miles) in under 6:50.
But why can I never get to my maximum heart rate ???
I have reached 185bpm while running the 5km, but lately I havn't been able to get close to even that ! I am suppost to have a max of over 200bpm, but why lately do I struggle to get to over 165bpm !!!?
Is there anyway to get close to my max ? and am I suppost to beable to ? I've been cycling alot lately, and is it really needed? Because I want to be on top form for the cycling season ahead, and I need to know if I am far behind, or not !

Thanks !

It seems that the type of exercise that you are doing is aerobic and with this type you will never get to your max. If you must go for max then try anaerobic exercise.