Consider this the opposite problem of not being tall enough to go on the ride.
Though it is possible to reserve a bulkhead or an exit row in advance, there is no need to pay extra for being a human being. It is possible to ask airline staff for—and be granted—a seat that has extra legroom right before boarding without paying a fee.
Most gate agents are more than happy to accommodate tall passengers - and surprise! they are people, too.
Generally, it does depend on availability and the gate agent, but the exits rows are often up to the airline's discretion.
Passengers likely to reserve an exit-row seat are also likely to be upgraded, meaning it is likely to be more available than a traditional seat closer to boarding.
Of course, being tall is subjective, but as long as you're heads and shoulders above everyone else, it's a safe bet that the request will be honored.
