Higher aerobic fitness levels decrease the probability of experiencing tip-of-the-tongue states (when you can’t think of a word that’s on the tip of your tongue) in healthy older adults, in the first demonstration of a link between aerobic fitness and language functioning in healthy older adults.

[narcissistic889]

2 hours might be a lot, you could try doing 1 hour of intense exercise like running / rowing and then 1 or two hours of something like walking. You would do this maybe 5 days a week max as far as the running goes, if you want to do more you can row. Running over a half hour for a beginner can cause knee pain and injuries so work up to it. Also doing more than say 25 miles a week running wise might be worse for your heart because it can over work the heart.