The advice given to adults buying a first telescope is usually the advice written for children with the prices raised, and the two buyers actually differ in ways that change the recommendation: budget, patience and what happens after the first month.
Adults tolerate more setup and want more aperture
A child needs an instrument that works in a minute. An adult will usually accept a few minutes of assembly and will be frustrated much sooner by an aperture that cannot show what the books describe. That pushes the sensible recommendation up from a tabletop instrument to a floor standing dobsonian of 150mm or 200mm.
Buy for the second year, not the first
The commonest adult pattern is a small telescope bought carefully, outgrown within a year, and replaced at more total cost than one better instrument would have been. If the interest is real, an instrument you will still want in three years is cheaper. If it is untested, binoculars cost far less than either.
Comfort matters more than anyone admits
An adjustable observing chair, a red torch and somewhere to put eyepieces down decide whether a session is twenty minutes or two hours, and adults are more likely than children to abandon a session that is physically uncomfortable. Budget for those alongside the instrument rather than afterwards.
What to actually buy
A 150mm to 200mm dobsonian if you can store and carry one; a 130mm tabletop, at $305.00 here, if you cannot; a small maksutov or refractor if it must live in a cupboard and work in two minutes. All three are real answers and the constraint that decides between them is your home rather than your budget.
Questions people ask about telescope
What is the best beginner telescope for adults?
A dobsonian of 150mm to 200mm if you can store and carry one, a 130mm tabletop otherwise. Both are genuinely capable instruments.
How much should an adult spend on a first telescope?
Enough for an instrument you will still want in three years, which usually means the three hundred to six hundred dollar range rather than the bottom of the shelf.
What is a good telescope for adults?
The largest aperture you will carry outside, on a mount that settles in a couple of seconds. Everything else is secondary to those two.