I've never been to Marlow, but from what I've found out online, it seems to be very similar to the town I grew up in in south west England (in terms of size, population, amenities etc.).
From census data, it would seem that the town is typically suburban, mostly populated by families with dependent children and by pensioners, with a fairly low proportion of young, single people (only 13% of households have just one adult, the other 87% consists of families with children, two adults living together and pensioners).
While Marlow does have several pubs and restaurants, it doesn't seem to have much of a nightlife apart from that. As far as I can tell, there are no bars, nightclubs or movie theatres in the town! I believe there is a small theatre that seems to host local amateur productions and shows and there are a few clubs and societies to join, but really, if you're looking for more of an adult-oriented social life (rather than family/child-oriented), you'd probably have to travel into London or to a different nearby town.
As english.bloke mentioned, there are other towns nearby with more amenities. High Wycombe is only 5 miles from Marlow, but has about 90,000 people (compared to 14,000 in Marlow); Reading is 25 miles to the south west and is even larger (143,000 people) and London is 33 miles to the east.